***Useful Information For The Working Sparky***

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17th EDITION REQUIREMENTS FOR THE TESTING OF RCDs :

The 17th Edition of the Wiring Regulations (BS 7671: 2008) will introduce a number of new requirements for the installation of
RCDs, therefore it is timely to look at the requirements within the17th Edition for verification of RCDs. The continuing effectiveness of these RCDs needs to be confirmed periodically. This article discusses the verification required where RCDs are
used to provide automatic disconnection of supply in the event of a fault and additional protection. It should be stated at this point that the 17th Edition does not introduce any significant changes in the requirements for the testing of RCDs even where they are installed to provide automatic disconnection in the event of a fault ,

Use of RCDs to achieve automatic disconnection in case of a fault :
411.3.2.1 requires (in most cases) that a protective device shall interrupt the supply to a line conductor of a circuit or equipment in the event of a fault of negligible impedance between said line conductor and an exposed conductive- part or a protective
conductor for the circuit or equipment within the appropriate required disconnection time. A disconnection time of 5 seconds
for distribution equipment and final circuits of rating exceeding 32A is permitted by 411.3.2.3. Similarly, a disconnection time of 1 second for distribution equipment and final circuits of rating exceeding 32 A is permitted by 411.3.2.4. : 411.3.2.2 states that the maximum disconnection times of Table 41.1 shall be applied to final circuits not exceeding 32 A. Table 41.1 gives the maximum
disconnection times for final circuits not exceeding 32 A of varying nominal voltages forming part of an
installation having either TN or TT system earthing. These disconnection times may be met by the use of fuses, circuit breakers (formerly known as MCBs) or RCDs. is used to meet the requirements of 411.3.2.2, that is, to provide the required disconnection time, the maximum values of earth fault loop impedance in Table 41.5 may be applied. The maximum permissible earth
fault loop impedances (Zs) to ensure RCD operation for non-time delayed RCDs protecting final circuits not
exceeding 32 A are given in Table 41.5, a new table introduced in the 17th Edition, which is reproduced below.
Where an RCD is employed to achieve the disconnection time required by Table 41.1, it is necessary to satisfy
ourselves that the maximum earth fault loop impedance (Zs) stated for a particular sensitivity of RCD in Table 41.5 is not exceeded in the circuit to which they provide protection. This is in effect the same procedure that we applied in earlier editions where fuses
or circuit breakers were used to achieve the necessary disconnection time and indeed continue to apply for fuses and circuit breakers in the 17th Edition. Regardless of which type of protective device is used to achieve the disconnection times required by Table
41.1, whether fuse, circuit breaker or RCD, there is no requirement to confirm that the required disconnection time can be achieved by testing the protective device. Rather, we confirm that the earth fault loop impedance of the protected circuit does not exceed the relevant tabulated maximum earth fault loop impedance for the type / sensitivity of the protective device intended to provide
the required disconnection time.

Maximum earth fault loop impedance (Zs) to ensure RCD operation in accordance with Regulation 411.5.3 for non-delayed RCDs to BS EN 61008-1 and BS EN 61009-1 for final circuits not exceeding 32 A

( 411.3.2.2 ) 230v
TN- Systems : The maximum disconnection time stated in table 41.1 shall be applied to final circuits Not-Exceeding 32Amp
( 411.3.2.3 )
TN- Systems : in a TN-system, a disconnection time Not exceeding 5sec is permitted for a distribution circuit and for a circuit Not covered by Regulation 411.3.2.2 ,
( the table you require TT-systems 41.5 p-50

Resistivity :

Double cable length – Double Conductor Resistance to 1.6 Ω, but halve insulation resistance to 50 MΩ
Halve . CSA – double conductor resistance to 1.6 MΩ, but insulation resistance is unaffected and remains 100 MΩ

Resistivity :
A twin cable has a Phase to Neutral résistance value of 100MΩ and an individual conductor résistance values of ( 0.8Ω )
Determine the values if the cable ….
(a) was double in length ,
(b) length as the same but the conductor cross-section areas was halved ,
Conductor Résistance
This is a function of the resistivity of the conductor material :
In other words , résistance is directly proportional to length and inversely proportional to area ,
So doubling length or halving the area will both double résistance , try it with some values ,

Let’s say the original length is 40m and the area is 2mm2 . The equation then , is :
0.8 = p x 40 ÷ 2 ( 0.8 x 2 ÷ 40 = 0.04 ( ignoring the units )
Double length : R = 0.04 x 80 ÷ 2 = 1.6Ω : / Halve area : R = 0.04 x 40 ÷ 1 = 1.6Ω
Beware the question that asks what happens if the diameter is varied , because is proportional to the diameter squared ,
Doubling diameter will increase the area by four times; halving the diameter will quarter the area ,
Insulation Résistance :
The Insulation between two conductors is considered to act as a ( Series of many high résistance in parallel )
Résistance ( because of the greater number of apparent parallel paths ) Taking the insulation résistance of the original length as R1 ,
Adding an identical extra length is like adding a second R1 in parallel , So :

…….... 1 ……..... 1
….. ─── = ─── so R1 = Rtotal = 100MΩ ( in the first instance )
……....Rtotal … R1

………………………. ……......... 1 ……..... 1……...... 1……...... 2
With double the length ….. ─── = ─── + ─── = ─── so new Rtotal = 50MΩ
…………………………......... Rtotal …... 100 ….... 100…...... 100

Changing the conductor CSA , should have no effect on the insulation résistance for the same value of voltage applied ,

Insulation Resistance Values
0.00 MΩ = dead short :
0.08 MΩ = low insulation resistance fault :
>200 MΩ = healthy circuit :

Notes: ensure all neon's are removed or isolated before commencing testing, as these will make test results appear low during insulation resistance testing.

Notes: Neon's will cause false readings, as will emergency or discharge lighting, so ensure these are all disconnected prior to commencing tests.

Prospective short circuit current (PSC) testing

The prospective short circuit or fault current at any point in an electrical installation is the current that would flow in the circuit if no circuit protection operated and a complete (very low impedance) short circuit occurred. The value of this fault current is determined by the supply voltage and the impedance of the path taken by the fault current. Measurement of PSC can be used to check that protective devices within the system will operate within safety limits and as per the safe design of the installation. PSC is normally measured between the phase and neutral at the DB or at a socket outlet.

 

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The 17th Edition of the IEE Wiring Regulations (BS 7671:2008) places much greater emphasis on the use of RCDs.
It is well-known that most circuits feeding 13A socket-outlets now require RCD protection but equally important are requirements for additional protection of wiring concealed in walls or partitions, which includes lighting circuits and their concealed switch wiring. This means that the vast majority of domestic circuits, power and lighting now require 30mA RCD protection :
There are also important requirements to minimise nuisance tripping and collateral risks due to a tripped RCD affecting other circuits, such as lighting.

Socket-outlets :
Rule 411.3.3 calls for additional protection by means of a 30mA RCD for all socket-outlets with a rated current not exceeding 20A for use by “ordinary persons”. The only exceptions allowed are for socket-outlets for use under the supervision of skilled or instructed persons (e.g. some commercial/industrial locations) or a specifically labelled socket provided for connection of a particular item of equipment (such as a freezer). :
This rule clearly covers the vast majority of domestic circuits feeding 13A socket-outlets, and any other socket-outlets (5A, 15A etc.) up to 20A. There is also a requirement for RCD protection of circuits feeding mobile equipment with a current rating up to 32A for use outdoors. :

Cables in walls or partitions
Rule 522.6.7 calls for RCD protection of wiring concealed in walls or partitions. All concealed wiring at a depth of less than 50mm now requires protection by a 30mA RCD unless it is provided with earthed mechanical protection, for example by metallic conduit or trunking. This applies to many lighting circuits and their switch wiring, including those installed in previously defined a “Safe Zones”. :

There is a further requirement for protection by means of a 30mA RCD where cables are concealed in walls constructed with metal stud partitions, irrespective of the depth from the surface, unless provided with protection in the form of earthed metallic covering, trunking, conduit or other mechanical protection so as to avoid damage to the cable during installation or construction of the wall. :
Special locations :

Rule 710.411.3.3 calls for RCD protection of all circuits in specific locations such as those containing a fixed bath or shower. This means that, in bathrooms or bedrooms with en-suite facilities, circuits feeding lighting, heating and showers must have RCD protection. :
Other “special installations and locations” as defined in Part 7 of the Regulations are also required to have RCD protection. These include swimming pools and saunas, agricultural premises, caravans and caravan sites, floor and ceiling heating systems. :

Sub-division of circuits :
Rules 314.1 and 2 require that every installation should be divided into circuits as necessary to avoid danger and minimise inconvenience in the event of a fault. Designers are required to reduce the possibility of unwanted RCD tripping due to excessive protective conductor currents but not due to an earth fault. :
Separate circuits may be required for parts of the installation which need to be separately controlled in such a way that they are not affected by the failure of other circuits. The appropriate subdivision should take account of any danger arising from the failure of a single circuit, for example an RCD trip causing the disconnection of an important lighting circuit. :

This affects the configuration of the protective devices in a consumer unit. For example if a number of circuits are protected by a common 30mA RCD, lighting circuits need to be spread over more than one RCD. :
Rules 314.1 & 2 also call upon the designer to take steps to reduce the likelihood of unwanted RCD tripping due to excessive protective conductor currents, other than earth faults. :
Typical situations would include IT equipment with certain types of radio frequency interference suppression, and certain types of heating equipment. The cumulative effect of such loads can produce a standing earth leakage current that is beyond the threshold point of a normal 30mA RCD. However this situation is becoming more common in residential environments. :

Earth loop impedance ( 2392-10 )
It should also be noted that Chapter 41 of the Regulations includes revised earth loop impedance tables based on a nominal voltage of 230V (Previously 240V). This results in slightly lower values of earth loop impedance and could, in some situations, mean that RCDs will be required to achieve the required disconnection time where previously overcurrent protection devices would be considered adequate. :

17th Edition IEE Wiring Regulations :

Key Changes : RCD Protection to Socket Outlets ,

• Socket outlets rated not exceeding 20 A and intended for general use by ordinary persons must be protected with 30 mA RCDs(Residual Current Devices). This means that general purpose sockets in domestic and similar properties must have RCD protection. An exception can be made for socket outlets for specific purposes e.g. domestic freezer circuit, this socket should be suitably labelled or otherwise identified.
• External sockets rated not exceeding 32 A must also have 30 mA RCD protection.
Installation of cables – RCD Protection Requirements :
• Cables that are buried less than 50mm into a wall or partition and are not enclosed in earthed metallic covering or have mechanical protection capable of resisting nails or screws should be protected by a 30 mA RCD as well as being installed in the ‘safe zones’ as previously permitted.
• Similarly, irrespective of depth of cable, cables that are installed in metal framed walls require 30 mA RCD protection if not otherwise protected by earthed metallic covering. :

The above requirements do not apply to installations where the installation is intended to be under the supervision of a skilled or instructed person, such as in office buildings, large retail outlets and industrial premises. :

Bath/ Shower Rooms (containing a fixed bath or shower) :
• All circuits within a bathroom must have RCD (30mA) protection. Where this is provided and main equipotential bonding is used in the installation then supplementary equipotential bonding is not required.
• Bathrooms being modified or refurbished can either have their supplementary equipotential bonding extended or can be rewired with the installation of RCDs.
• Zone 3 has been removed
• 13A sockets in bathrooms are allowed providing they are installed at least 3m from the edge of the bath and protected by a 30mA RCD.
Under Floor Heating Systems :
Underfloor and ceiling heating systems are now covered as a special location/installation.
• A plan of the heating system shall be provided for each system (showing location, area, rating details, descriptions for use etc). A copy of the instructions for use should be fixed adjacent to the distribution board supplying the heating.
• Heating systems which do not have an exposed conductive covering or mesh must have installed on site a suitable exposed conductive part installed above the heating element . This could be in the form of an earthed metallic grid with spacing of not more than 30mm.
• A 30mA RCD must be used as the disconnection device.
• Heating systems of Class II (Double insulated) construction shall be provided with 30mA RCD protection.
•Floor heating systems in bathrooms the metal sheath, metal enclosure or fine mesh metallic grid should be connected to the protective conductor of the supply circuit.
Maximum Zs values
•There are new values based upon a nominal voltage of 230v and not 240v hence the values have been slightly reduced (i.e. 32A Type B - MCB was 1.50 now 1.44).
A new table has been provided giving the maximum values of earth fault loop impedance for RCDs.
Voltage Drop

•The new regulations now provide different voltage drop values for installation supplied from a public supply and private supply (i.e. Own generation). For a public supply the maximum values are 3% for lighting and 5% for other uses, for a private supply the maximum values are 6% for lighting & 8% for other uses.
Disconnection Times
•Final circuits not exceeding 32A shall have a maximum disconnection of 0.4 seconds for a TN-S or TN-C-S (PME) earthing arrangements.
•For TT systems the maximum disconnection time is 0.2 seconds, however a statement is included in the table (41.1) which states "Where disconnection is achieved by an overcurrent protective device, and the protective equipotential bonding, or main equipotential bonding, is correctly installed, the maximum disconnection times applicable to a TN system may be used."
New Sections on:

• 559 - Luminaries and Lighting
• 709 - Marinas and similar locations
• 711 - Exhibitions, Shows and Stands
• 712 - Solar Photovoltaic (PV) Power Supply Systems
• 717 - Mobile or Transportable Units
• 721 - Caravans and Motor Caravans
• 740 - Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses

 

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17th Edition – ( this will help you with your 17th Chaps ,

Part 1: Scope, Object & Fundamental Principles ,

* (134.2.2 ) Designer of Installation responsible for specifying the interval to the first Periodic Inspection ,
* ( 135.1 ) Now makes a Positive Recommendation that every electrical Installation is subject to Periodic and Testing , in Accordance with Chapter 62 : p-162

Part 2 : Definitions ,
“ Competent Person “ ↔ p-22

Part 2 : Definitions , ↔ p-24
* Exposed Conductive part , A Conductive part of Equipment which can be touched and which is not live but which can
Become live when basic insulation fails , Example ( Metal Switch Plate , )
Part 2 : Definitions , ↔ p-24
• Extraneous-conductive parts , and its associated definition , remain unchanged :

************
* Line Conductor ( Replaces Phase Conductor Line is the Internationally used tem ) Do Not Confuse Line Conductor which can be a Neutral Conductor :

Chapter 41 : RCDs ,

* RCDs are now recognised as giving additional protection ( this term is now used instead of Supplementary Protection ) ←←←
* RCD now required for all general use socket-outlets rated up to 20A , allows for 2 Exceptions ←←←
(1) Socket-outlet used under supervision of skilled or instructed persons :
(2) Socket-outlet suitable identified for connection of particular item of equipment :
* To be recognised as giving additional protection The RCD must be rated at 30mA or Less and operate within 40mS
When tested at ( 5 x rated operating current )
Chapter 41 :
Revised Disconnection Times :
* TN-systems – 0.4 seconds ( Final Circuits up to 32Amp : ←←←
* TT-systems – 0.2 seconds ( Final Circuits up to 32Amp - Allows for 0.4s where all Protective bonding in place and
Disconnection is achieved by Overcurrent Device )
* Distribution circuits and circuits not covered by table 41.1 ( TN- = 5 seconds & TT = 1 second ,
* Supplementary bonding can be used were Disconnection Times can Not be Met . ←←←

Chapter 52 :
Selection & Erection of Wiring Systems :

* Chapter 52 now includes reference to Busbar Trunking systems and Powertrack systems :
* Max Value of Voltage Drop in Consumer’s Installations has Changed – Appendix 12 . p-358
Volt drop between origin and load terminals in LV system to be Less than ;
2392-10 ( Public Supply : Lighting 3% …….. Other Uses 5% ,
Private Supply : Lighting 6% …….. Other Uses 8% ,
( These Replace the Current 4% Requirement ) ←←←←←←←←

Chapter 55 :
Luminaires & Lighting ( 559 ) Regs
* Maximum circuit rating 16A for B15 , B22 , E14 , or E40 Lamp Holders ,
* Through wiring only permitted where light is designed for this ,
Chapter 55 :
Luminaires & Lighting ( 559 ) Regs
* 559 applies to selection & erection of luminaires & lighting installations fixed Installations and highway power supplies & street furniture ,
* Outdoor lighting includes : - Roads , Parks , Car-Parks , Gardens , Sporting Areas , Monuments , Floodlighting , Telephone Kiosks ,
Bus Shelters , Advertising Panels , Road Signs & Road Traffic Signals ,
• Excludes , Distributors Equipment & Temporary Festoon lighting ,

Part 6 :
* New part 6 Inspection & Testing Table 71A ↔ Now known as ( Table 61 p-158 )
-&- will ask you this one , ( 0.5MΩ SELV or PELV at 250 volts ) ←←←←

Chapter 62 :
Periodic Inspection & Testing
621.5 : Periodic Inspection & Testing shall be undertaken by a Skilled Person , Competent in such work ,
* Proof of Competence may be required ,

Section 701 : Bathrooms ,
* Section 7 Special Installations or Locations :
* Section 701 Locations, containing a bath or shower ,
* Zone ( 3 ) has been Removed : ←←←←←
* Suitable Equipment can be within 600mm of a bath ,
* Excluding 13amp Sockets to BS-1363 ( p-229 ) which must be 3 Meters from edge of bath or shower , -&- ,
* All circuits to be RCD Protected ,
* Supplementary bonding is NOT required – Provided any Required Protective Equipotential bonding has been installed ,

Part 7 :
Regulation ( 415.2 ) Supplementary Equipotential bonding : in relation to Section 701 , i.e. Locations Containing bath or Shower ←←:

Section 704 : Construction & Demolition Sites :
Section 705 : Agriculture & Horticulture :
• in both sections the reduced disconnection times of ↔ ( 0.2s ) ↔ and ↔ ( 25v ) ↔ Equation have been Removed : ←←←←

Section 708 : Caravan & Camping Parks :
* Sockets-Outlets must be provided individually with overcurrent and RCD protection for each pitch outlet : -&-
( Previously 1 RCD was allowed to protect not more than 3 pitch outlets ,

Tables 41.2, 41.3, 41.4

* If the measured Zs value exceeds 80% of the given values, a more precise measurement may have to be made to satisfy the requirements of BS-7671 . p361 :
* BS-7671 does not give maximum Zs values for BS 3871 mcb's. :
* If the maximum Zs value for a circuit in a TN- system cannot be met, the circuit may be protected by a 30ma RCD . 531.3.1
* If the maximum Ze value for a TN- system cannot be met, the installation may be protected by a 100ma RCD and treated as a TT- system. 531.3.1, 411.5.1, 411.5.2, 411.5.3 :

RCD :
the maximum disconnection time allowed for a RCD protected socket for a caravan/tent pitch :
Please refer to BS 7671:2008 Reg 708.553.1.13, this refers to Reg: 415.1.1, ( 30mA RCD 40mS at 5 x 30mA. )

17th Edition requirements for the testing of RCDs :

The 17th Edition of the Wiring Regulations (BS 7671: 2008) will introduce a number of new requirements for the installation of RCDs, therefore it is timely to look at the requirements within the 17th Edition for verification of RCDs.
The continuing effectiveness of these RCDs needs to be confirmed periodically. This article discusses the verification required where RCDs are used to provide automatic disconnection of supply in the event of a fault and additional protection. It should be stated at this point that the 17th Edition does not introduce any significant changes in the requirements for the testing of RCDs even where they are installed to provide automatic disconnection in the event of a fault.
Use of RCDs to achieve automatic disconnection in case of a fault 411.3.2.1 requires (in most cases) that a protective device shall interrupt the supply to a line conductor of a circuit or equipment in the event of a fault of negligible impedance between said line conductor and an exposed conductive- part or a protective conductor for the circuit or equipment within the appropriate required disconnection time. A disconnection time of 5 seconds for distribution equipment and final circuits of rating exceeding 32A is permitted by 411.3.2.3. Similarly, a disconnection time of 1 second for distribution equipment and final circuits of rating exceeding 32 A is permitted by 411.3.2.4.

Does the 17th Edition require a new test for RCDs ?

The rumour seems to have originated from Note 2 of Table 41.1 of the 17th Edition, with gives maximum permitted disconnection times for final circuits rated at up to 32A. The note states that: ‘Where compliance with this regulation is provided by an RCD, the disconnection times in accordance with Table 41.1 relate to prospective residual fault currents significantly higher than the rated residual operating current of the RCD.
BS 7671: 2008 (IEE Wiring Regulations 17th Edition) was published in January and comes into effect on 1st July. A rumour has been circulating amongst electrical contractors that the 17th Edition requires RCDs to be subjected to a test at twice their rated residual operating current (2 x I∆n ). Is this the case ?


As explained in this article, the familiar currents of 0.5 x I∆n , 1 x I∆n, and 5 x I∆n, (as applicable) should be all that are needed when testing RCDs in the vast majority of installations, as is the case under the 16th Edition.

A 2 x I∆n, test would be needed only in exceptional circumstances. But, even where this is the case, it does not necessarily mean that an RCD test instrument having a 2 x I∆n, test setting is required.

The rumour seems to have originated from Note 2 of Table 41.1 of the 17th Edition, with gives maximum permitted disconnection times for final circuits rated at up to 32 A. The note states that: ‘Where compliance with this regulation is provided by an RCD, the disconnection times in accordance with Table 41.1 relate to prospective residual fault currents significantly higher than the rated residual operating current of the RCD (typically 2 x I∆n ).’ However, Note 2 does NOT mean that a 2 x I∆n test is required.

 

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-&- ( 2391-301 Inspection, Testing and Certification of Electrical : Installations report – ( -&- March 2009 :

It would appear that candidates are still unaware that a working knowledge of Guidance Note 3 and BS 7671:2008 is required to achieve success in this qualification. Many candidates demonstrated significant gaps in both technical and underpinning knowledge of the subject matter. In particular the interpretation of information and test results and the validation process for test results are areas of concern.

From the information given by candidates it is apparent that they may be aware of the need for inspection and testing, but have little understanding of the reasons why it is done or the interpretation of the results obtained.
Many candidates did not display the required knowledge when answering the questions and this would suggest they do not have the necessary knowledge, understanding and experience when entering this qualification.

Use of correct terminology :
Correct terminology must be used when answering questions. Candidates continue to use incorrect terminology. This does indicate that candidates are not aware of the underlying requirements and processes. Typically candidates still referred to a periodic inspection and testing report as the type of inspection and the Electricity at Work Regulations is still incorrectly referred to as the Electricity at Work Act. Candidates also continue to use incorrect titles for documents and publications and to use inappropriate titles for the forms of certification
Documentation :
Some candidates were unable to identify the correct title of documents for certification, and many still refer to a Periodic Inspection Certificate. Candidates were unable to correctly identify the
Schedules by title with a Schedule of Items Inspected and a Schedule of Tests being common incorrect alternatives.
Questions which required candidates to identify where information is to be recorded on the forms of certification produced results which appear to indicate the candidates are not familiar with both the compilation and the content of these forms.
Many candidates did not consult with the third party (licensing authority) when determining the extent and limitations.
Inspection :
Question 22 asked candidates to identify three particular areas for investigation during inspection due to the nature of the location in the kitchen, laundry and residents rooms. The responses to this question were exceptionally poor with many candidates simply listing items such as sockets and switches for all locations giving no indication of the particular areas of investigation. Others included tests and many demonstrated a lack of understanding of the requirements for the locations. Many believed that some type of non-specific bonding was required.
Considering the information provided in the scenario there were very few candidates who identified inspection related to corrosion, appropriate IP ratings damage and the like. In the residents rooms many candidates considered the equipment being PAT tested etc as appropriate items for their inspection.
The response to this question generally indicated a lack of understanding of the inspection process and the information provided in GN3 related to the inspection of installations.
Question 4 required candidates to identify reasons why a survey would be required before a periodic inspection could be undertaken. Very few candidates were able to identify the relation to information not being available. Most identified events that could give rise to a periodic inspection being required.
Testing :
The common misunderstandings identified above show that ring final circuit testing is still a problem for many candidates. There is also some confusion as to the required tests fro particular circuits with many quoting the standard list, and the range of values expected for the tests undertaken. The test process and the expected results are fundamental to the requirements of those undertaking inspection and testing and for the candidates to complete the practical assessment.
Calculations :
Many candidates had problems with calculations related to the inspection and testing process. Cumulative insulation resistance values, determining values for stage 2 and stage 3 of the ring final circuit continuity test from given information caused some difficulty. These calculations are typical of the type of evaluations which may be required during the verification of test results. As these are fundamental to the activities of initial verification and periodic reporting such calculations should be within the abilities of the candidates. It would appear that a number of candidates do not understand the effects of resistances in series and parallel.

Describing test procedures :
When describing how to carry out a test, candidates were often confused as to what was required, unable to describe a logical approach and rarely used large clear diagrams to assist with their description. 2391-
Drawings and labels :
Question 25 required candidates to provide a fully labelled diagram of the earth fault loop path for a radial circuit. The scenario identified the system as TN-S. Whilst some candidates used the incorrect system there was a general lack of clear drawing and labelling.

Section A :

In Section A there were many fundamental errors identified in candidate responses. Typically many candidates

• identified a shock risk when testing main protective bonding conductors and not the tripping hazard. If the procedure is correct (isolation of the installation) there is no shock risk.

• could not correctly identify the reason for carrying out a continuity of ring final circuit test.

• could not identify special locations which were classified in zones; this including listing locations such as caravan sites and construction sites.

• were unaware of the IP requirement for Basic Protection with most examples related to ingress of liquids.

• were unable to determine the recorded RA value from given data, many adding the three values in parallel.

• did not know why R1 + R2 cannot be determined using Zs – Ze. Despite this information being given in Question 16 of Section A, many then went on in Section B to determine R1 + R2 using this incorrect method.

• were unable to identify the connection points for the instrument leads when measuring Ze when using a three lead test instrument.
• could not determine the maximum Zs for a 300 mA RCD to meet the requirements of BS 7671
• could not correctly determine the maximum permitted voltage drop for given circuits. Many used 16th edition values and/or determined voltage at equipment terminals.

Section B :
In Section B there were some areas where candidates were unable to demonstrate their understanding of the subject.

Many candidates were unable to

• identify operational aspects which would affect the inspection and testing activity with many simply identifying locations which were given in the scenario without identifying the aspect.

• identify the correct test sequence and relate instruments and ranges for the tests. For a radial final circuit the candidates included main protective bonding conductors, ring final circuit continuity and polarity with an approved voltage indicator in the dead tests, and PFC and RC in the live tests.

• describe the ring final circuit continuity test with may carrying out Stage 2 & 3 linking one pair (L1 & N2) and testing across the other pair for each test. Some included this as an extra stage wasting time and effort. A number were unable to determine the expected values.
• determine the calculated values of R1 and R2 correctly with a surprising number incorrectly using Zs – Ze despite the information in Part A that this method could not be used. Most candidates failed to appreciate that two of the circuits were ring final circuits and therefore failed to divide their result by 4.

Exam technique – time management :
Time management for candidates is important to ensure they have an opportunity to achieve the best possible result. Considering the number of marks available for each question and using this determine the extent and depth of the answer required would be useful. 2391-
As a guide, candidates should spend approximately one minute on an answer for each possible mark to be awarded. A question worth three marks for example should take approximately three minutes to complete. However many questions in Section A will take considerably less than this.

Exam technique – read the question
Careful reading of the question is important. Many answers did not include the information requested and candidates often provided answers which did not correspond to the question posed.
Candidates often did not answer the questions in both Sections A and B of the paper in relation to the given information and this often resulted in the loss of marks. Candidates must read the information given in the question. 2391-

 

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C&G 2382. 17th Edition ( BS7671:2008 ) Examination :

1. The Regulations (BS7671:2008) do NOT apply to
a. Residential Premises
b. Industrial Premises
c. Lightning Protection
d. Street Furniture
2. The Regulations do apply to
a. Offshore Installations
b. Mines & Quarries
c. Lift Installations
d. Low Voltage Generators
3. Which of the Following documents are deemed Non- Statutory
a. BS7671:2008
b. EAWR 1989
c. HASAW 1974
d. ESQCR 2002
4. Parts 3 – 7 of BS7671:2008 are explained in rudimentary terms within
a. Chapter 13
b. Chapter 12
c. Part 3
d. Appendix 5
5. Basic protection is defined as
a. Protection against shock under fault conditions
b. Protection against shock under fault free conditions
c. Protection against contact with live parts under fault free conditions
d. Protection against faults under sound electrical conditions
6. Equipment in which protection against electric shock does not rely on basic
insulation only is described as
a. Double Insulated Equipment
b. Class I Equipment
c. Class II Equipment
d. Class III Equipment
The7. The Earthing System illustrated in Figure 1 below would be identified as a
a. TN-S
b. TT
c. TN-C-S
d. IT
8. A Voltage of 250Volts AC (rms) would be defined as
a. Band I
b. Extra Low Voltage
c. High Voltage
d. Low Voltage
9. In determining Maximum Demand, ‘Diversity’ may be applies, which is
a. Taking the sum of all the protective devices from any CCU
b. Taking into account that not all loads will be switched on at the same time
c. Taking into account that all loads doubtless will be engaged at the same time
d. Ensuring that an economical and reliable design preference is utilised.
10. Every Installation is divided into circuits in order to
a. Ensue simplicity of isolation
b. Comply with European Standards
c. Avoid hazards and prevent inconvenience in the event of a fault
d. Allow individual energising of circuits which are not isolated
11. A building made entirely out of wood would be categorised for External Influences as
a. CA2
b. CA1
c. CB3
d. CB4
12. The Maximum Disconnection time for an a.c. TN circuit rated at 230V is
a. 0.04 seconds
b. 0.1 seconds
c. 0.4 seconds
d. 0.2 seconds
13. The Maximum Zs for a BSEN60898 Type C circuit breaker rated at 16Amps with
a 0.4second disconnection time is
a. 2.87Ω
b. 1.44Ω
c. 0.72Ω
d. 1.15Ω

14. For a TT System the Maximum earth fault loop impedance for a 100mA
BSEN61008-1 RCD in a 230Volt circuit is
a. 500Ω
b. 460Ω
c. 167Ω
d. 100Ω
15. Where, on electrical equipment, must the symbol in figure 2 be present
Figure 2
a. Where basic and supplementary earthing is present on an appliance
b. Where supplementary earth-bonding to an appliance is not present
c. Where electrical equipment has basic insulation only
d. Where Class I equipment is served from a sub-main CCU
16. Where Basic Protection is employed in the form of a barrier or enclosure, any
horizontal top surface must meet a protection level of at least
a. IPDXX
b. IP2X
c. IPXX3
d. IP4X
17. Except if made from adequate material, a luminaire rated at 200Watts should be
located away from combustible material by
a. 0.3m
b. 0.5m
c. 0.8m
d. 1.0m
18. To avoid burning, a non-metallic part intended to be touched but not hand held
cannot exceed
a. 80°C
b. 85°C
c. 90°C
d. 95°C
19. In relation to Voltage Disturbances, the resistance of the earthing arrangement
at the Transformer is referred to, within the area of symbols, as
a. RA
b. RB
c. RD
d. RE
20. Every core of a cable shall be identifiable at its terminations and preferably
throughout its length by
a. colour code only
b. letter code only
c. number code only
d. one or more of the above
21. An appropriate colour for a PEN conductor should be:
a. blue through its length with green markings at the terminations
b. green & yellow through its length with blue markings at the terminals
c. green & yellow through its length with brown markings at its terminals.
d. Green through its length with yellow markings at the terminals
22. A permanent label with the words ‘Safety Electrical Connection – Do Not
Remove’, complies with:
a. BS728
b. BS1363
c. BS951
d. BS423
23. A cable buried underground but not in conduit or ducting for mechanical
protection must incorporate
a. An earthed armour or metal sheath or both
b. A surface covering of 50mm thickness paving stones
c. A clear surface warning notice informing of its location
d. A PVC outer sheath
24. The de-rating factor for a cable surrounded by 50mm of thermal insulation is
a. 0.88
b. 0.78
c. 0.63
d. 0.51
25. In an L.V installation supplied directly from a public L.V distribution system the
maximum volt drop on a lighting circuit between the origin and any load point
should be no greater than
a. 6% Uo
b. 5% Uo
c. 4% Uo
d. 3% Uo

26. Every electrical inspection shall be accessible for inspection, testing and
maintenance purposes except for which of the following
a. A connection made in a junction box beneath floorboards
b. A connection made within a motor control unit
c. A connection designed to withstand fault current
d. A compound filled or encapsulated joint
27. The rated RCD operating current of such a device installed as a protection
against risk of fire in a TT system shall have a value of
a. 30mA
b. 100mA
c. 300mA
d. 500mA
28. The maximum prospective short circuit or earth fault current in a circuit should
not exceed
a. The operating current of circuit switching devices
b. The rated breaking capacity of any associated protective device
c. The design current of the circuit
d. The rated operating current of any RCD in circuit
29. Which of the following switching devices may be satisfactorily utilised for the
purposes of isolation?
a. BSEN60669-2-4
b. BSEN60669-2-3
c. BSEN60669-2-1
d. BSEN60669-1
30. When using bare conductors in extra low voltage lighting installations supplied
from a safety isolating transformer the minimum permissible cross sectional
area of conductors must be
a. 1.5mm2
b. 2.5mm2
c. 4mm2
d. 6mm2
31. Suspension devices for ELV luminaries must in any case be capable of
supporting at least
a. 5 Kg
b. 7.5 Kg
c. 10 Kg
d. 20 Kg
32. An automatic electrical safety service supply classed as medium break must, in
the event of losing the main supply, instate the safety service supply in a time
period of
a. between 0.15 & 0.5 seconds
b. between 0.5 & 5 seconds
c. between 5 & 15 seconds
d. greater than 15 seconds
33. The minimum value of Insulation Resistance for a 230Volt system must be
a. >0.25 MΩ
b. >0.5 MΩ
c. >1.0 MΩ
d. >2.0 MΩ
34. Correct Polarity must ensure that every ES lamp-holder have their outer or
screwed contacts connected to the neutral conductor, except for
a. E14 & E27 Lampholders
b. E14 & BSEN60895 Lampholders
c. E27 & BSEN61009 Lampholders
d. E11 & E24 Lampholders
35. To comply with PART 6 of BS7671, Periodic Inspection & Testing shall be
specifically undertaken by
a. A formally qualified Test Engineer
b. A person deemed as the ‘Duty Holder’ of the company carrying out the work
c. A expressly skilled person
d. A competent person
36. Zone 2 of a bathroom is restricted to the highest water outlet or the horizontal
plane lying above finished floor level by
a. 3.00m
b. 2.50m
c. 2.25m
d. 2.00m

37. In Zone 3 of a Sauna equipment must be able to withstand a minimum
temperature of
a. 100°C
b. 120°C
c. 125°C
d. 170°C
38. In marinas, equipment installed above a jetty or wharf, which is likely to
encounter water jets, shall be selected to comply with external influence levels
of
a. (AD4): IPX4
b. (AD5): IPX5
c. (AD6): IPX6
d. (AE6): IPX5
39. For a BS88-2.2 Fuse rated at 25A to obtain a 0.4sec disconnection time, it would
require a minimum prospective fault current of
a. 160A
b. 130A
c. 100A
d. 85A
40. A 30Amp Semi Enclosed BS3036 Fuse receiving a prospective fault current of
130A would disconnect in
a. 5.0sec
b. 1.0sec
c. 0.4sec
d. 0.2sec

Answers:
1. C Part 1 -110.2 Page 13
2. D Part 1 -110.1 Page 12
3. A Part 1 -114.1 Page 13
4. A Part 1 -120.3 Page 14
5. B Part 2 - DEFENITIONS
6. B Part 2 - DEFENITIONS
7. C Part 2 - DEFENITIONS
8. D Part 2 - DEFENITIONS
9. B Part 3 - 311.1 Page 38
10. C Part 3 - 314.1 Page 39
11. A Appendix 5 Page 319
12. C Part 4 - Table 41.1 Page 46
13. B Part 4 - Max Zs Tables - Part 4
14. B Part 4 - Table 41.5 Page 50
15. C Part 4 - 412.2.1 Page 55
16. D Part 4 - 416.2.2 Page 60
17. C Part 4 - 422.3.1 Page 67
18. A Part 4 - Table 42.1 Page 69
19. D Part 4 - 442.1.2 Page 80
20. D Part 5
21. B Part 5
22. C Part 5
23. A Part 5
24. A Part 5 – Table 52.2 Page 104
25. D Part 5
26. D Part 5
27. C Part 5
28. B Part 5
29. A Part 5
30. C Part 5
31. A Part 5
32. C Part 5
33. C Part 6 - Table 61 Page 158
34. A Part 6 - 612.6 Page 159
35. D Part 6 - 621.5 Page 162
36. C Part 6 - Page 169
37. C Part 7 - 703.512.2. Page 180
38. B Part 7 - 709.512.2.1.1 Page 193
39. A Appendix - Time/Current Graph - Page 248
40. C Appendix - Time/Current Graph -Page 245

Symbols :
In Rated current of the contacts - Expressed in amperes e.g. 100A.
I?n Sensitivity or residual operating current - Usually expressed in amperes e.g. 0.03A for 30mA

 

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Regulation 411.5.3 requires that for TT systems the
formula in 411.5.3 (ii) RA I∆n & 50 V.

RCD maximum Zs or RA values
……… maximum touch voltage
I∆n (A)………. 50V
0.01 …………. 5000Ω
0.03 …………. 1666Ω
0.1 ……………. 500Ω
0.3 ……………. 166.6Ω
1 ………………. 50Ω
3 ………………. 16.66Ω

Earth electrode resistances over 200Ω are likely to be unstable
( Measured Résistance should not exceed 100Ω ,

( RA I∆n ≤ 50 V : R ≤ 50v / 30mA , ( 50 ÷ 30 = 1667Ω
R ≤ 50v ÷ 160 = 0.31Ω ( 30mA RCD protects a.c Circuit rated residual current 30mA ,

411.5.4 : ( Zs x Ia ≤ Uo ) 32A = ÷ 230 = 0.13Ω
TT , 50v ÷ .3mA = 166.7 Ω , ( 30mA )
100mA = ) 50v ÷ 0.1mA = max Zs off 500Ω

612.9 : Earth fault loop impedance, Zs

This may be determined either by Direct Measurement at the further point of a live circuit OR by adding (R1 + R2) Ze

i.e. Zs = Ze + ( R1 + R2 ). In general, the Earth Fault Loop Impedance shall Not Exceed 100 Ω.

17th Edition Forms : 2392-10

1 Initial inspection and testing 2392-10

Forms 1 to 4 are designed for use when inspecting and testing a new installation, or an alteration or addition to an existing installation. The forms comprise the following:
1 Short form of Electrical Installation Certificate (To be used when one person is responsible for the design, construction, inspection and testing of an installation.)
2 Electrical Installation Certificate (Standard form from Appendix 6 of BS 7671)
3 Schedule of Inspections
4 Schedule of Test Results.
Notes on completion and guidance for recipients are provided with the form.

2 Minor works 2392-10
The complete set of forms for initial inspection and testing may not be appropriate for minor works. When an addition to an electrical installation does not extend to the installation of a new circuit, the minor works form may be used. This form is intended for such work as the addition of a socket-outlet or lighting point to an existing circuit, or for repair or modification.
Form 5 is the Minor Electrical Installation Works Certificate from Appendix 6 of BS 7671.
Notes on completion and guidance for recipients are provided with the form.

3 Periodic inspection 2391-10
Form 6, the Periodic Inspection Report from Appendix 6 of BS 7671, is for use when carrying out routine periodic inspection and testing of an existing installation. It is not for use when alterations or additions are made. A Schedule of Inspections (3) and Schedule of Test Results (4) should accompany the Periodic Inspection Report (6).
Notes on completion and guidance for recipients are provided with the form.

2392-10

Prospective short circuit current is the greater of the short-circuit current and earth fault current -&- :
Ze, the external impedance measured at the origin of the installation with the main bonding disconnected. -&- :

Continuity of protective conductors - Every protective conductor including bonding conductors shall be tested to verify it is sound and correctly connected :

Continuity of final circuit conductors - The sum of the resistance of the of the phase conductor (R1) and the protective conductor (R2 ) i.e. R1 + R2 , is to be inserted : This may be use, after temperature correction, by adding to Ze , to determine Zs.

Insulation resistance :

Equipment such as electronic devices shall, where necessary, be disconnected from the installation to avoid damage during testing. Where required, such equipment shall be tested separately.

17th Edition wiring regulations, explains : 2392-10

There is also a specific requirement for appropriate documentation for all installations.
Of particular interest to the health and safety manager, Regulation 134.2.1 requires that inspection and testing must be carried out by a 'competent person' to verify that standards have been met.
Importantly, a 'competent person' is defined as someone 'who possesses sufficient technical knowledge and experience for the nature of the electrical work undertaken and is able at all times to prevent danger, and where appropriate, injury to themselves and others'.
In practice, this means that inspection and testing should only be taken by experienced engineers that are qualified to the City and Guilds 2392 - 10 course 'Fundamental Testing, Inspection and Initial Verification'.
This course is now recognized as the qualification for competent persons carrying out initial inspection and testing of electrical installations.
For periodic inspection and testing, competent persons should successfully complete the C&G 2392 - 20 'Inspection, Testing and Certification of Electrical Installations' course in addition to the 2392 - 10 course.
Once the initial verification of the installation has been completed, which includes both inspection and testing, the regulations call for the issuing of an Electrical Installation Certificate, together with a schedule of test results and a schedule of inspections.
The certificate includes space for three signatures - the person responsible for the design, the person responsible for the construction and the person carrying out the inspection and test of the installation.
It should be emphasized that the signature for the inspection and test section is the person who actually carries out the inspection and test and not someone else who may be in authority.
In some cases, all three sections may require signature by the same person and this is perfectly acceptable.
However, the Electrical Installation Certificate should not be signed until any defects identified by the person responsible for inspection and test have been corrected.
An Electrical Installation Certificate (or a Minor Electrical Installation Works Certificate), stating the extent of the works covered, shall be issued once the inspector is satisfied that the works comply with the regulations.
Any defects found in related parts of the installation, not affecting the safety of the alteration or addition should be reported in writing to the person ordering the work.
If existing defects affect the new work then these defects need to be corrected before an Electrical Installation Certificate can be issued and before the new work can be put into service.
An example of this is where bonding or equipotential bonding is inadequate or omitted, as this would seriously affect the safety of the whole installation, including the new work.
The Electrical Installation Certificate should not be used for periodic inspections.
The 17th Edition regulations stipulate that the designer of the installation is responsible for specifying the interval to the first periodic inspection and test.
There is also the positive recommendation (Regulation 135.1) that every electrical installation is subject to periodic inspection and testing by a competent person (in accordance with Chapter 62).
For example, the IEE Guidance Note for periodic fixed installation test frequencies advise a maximum period of five years between inspections and testing for commercial offices, shops and hospitals - reducing to three years for industrial facilities, leisure complexes and theatres.
For some special installations, such as swimming pools, petrol stations and caravan parks, the maximum period between inspections and testing is one year.
This represents a substantial difference from the previous edition, which presumed that a programme of risk assessments, records and preventative maintenance could be adopted in place of periodic testing.
The Periodic Inspection Report form is only to be used for the inspection of an existing installation and should include both inspection and test results.
Again the extent and limitations of the report needs to be stated and recommendations of defects and their remedies should be made.
The report includes a numbering system for this purpose, as follows: 1 - Requires Urgent Attention; 2 - Requires Improvements; 3 - Requires Further Investigation; and 4 - Does Not Comply With BS 7671:2008 (although this does not necessarily imply that the electrical installation is unsafe).
A minor works is defined as 'work which does not include the provision of a new circuit'.
Testing is still essential and a number of tests are specifically identified as essential to confirm safety.
Also included on the form is space to allow the inspector to comment on the existing installation.

.

 

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17th Edition wiring regulations, explains :
“Earthing Arrangements “
1. Earthing Arrangements
2. In this section we are going to look at : -
The basics of shock .
Shock protection .
Class 1 & Class 2 equipment .
The three common earthing arrangements .
3. Earthing arrangements -
4. Definitions from Part 2 BS 7671
5. Bonding conductor A protective conductor providing equipotential bonding
6. Where protection against electric shock does not rely solely on basic insulation alone. Exposed-conductive parts being connected to a protective conductor within the fixed wiring of the installation. Class I equipment Class I insulation Single-layer insulation Live part Exposed conductive part
7. Class II equipment Where protection against electric shock relies on the application of additional or supplementary insulation. There is no provision for the connection of a protective conductor to exposed metalwork. Class II insulation Live part Two layers of insulation Exposed metalwork
8. Double insulation Double insulation (Class II) - Insulation comprising both basic insulation and supplementary insulation Symbol found on equipment
9. Earth The conductive mass of Earth, whose electric potential at any point is conventionally taken as zero
10. Earth Electrode A conductor or group of conductors in intimate contact with, and providing an electrical connection to earth
11. Earth electrode resistance The resistance of an earth electrode to earth
12. Earth fault current A fault current which flows to earth
13. Earth fault loop impedance The impedance of the earth fault current loop  starting and ending at the point of earth fault. Symbol Z Unit
14. The earth fault loop The earth fault loop starting at the point of fault consists of:
o The circuit protective conductor (c.p.c.)
o Consumers earthing terminal and earthing conductor
o For TN systems, the metallic return path
o For TT and IT systems the earth return path
o The path through the earthed neutral point of the
o transformer
o The transformer winding and phase conductor to point
o of fault
15. Earth leakage current A current which flows to earth, or to extraneous conductive parts, in a circuit which is electrically sound. This current may have a capacitive quality including that from the deliberate use of capacitors for noise filtration.
16. Earthed equipotential zone A zone within which exposed conductive parts and extraneous conductive parts are maintained at substantially the same potential by bonding, such that under fault conditions, the differences in potential simultaneously accessible exposed and extraneous- conductive parts will not cause electric shock.
17. Earthing Connection of the exposed conductive parts of an installation to the main earthing terminal of that installation
18. Basic contact (shock) Results from Making contact with parts of a circuit or system which are live under normal conditions
19. Earthing Connection of the exposed conductive parts of an installation to the main earthing terminal of that installation
20. Extraneous conductive part A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.
21. Fault A circuit condition in which current flows through an abnormal or unintended path. This may result from an insulation failure or a bridging of insulation. Conventionally the impedance between live conductors or between live conductors and exposed or extraneous conductive parts at the fault position is considered negligible.
22. Functional earthing Connection to Earth necessary for proper functioning of electrical equipment Table 51A Functional earthing conductors to be coloured cream
23. Contact of persons or livestock with exposed-conductive parts which have become live under fault conditions. Fault contact
24. Protective conductors A conductor used for some measure of protection against electric shock and intended for connecting together any of the following parts
o Exposed conductive parts
o Extraneous-conductive parts

17th Edition : Earthing & Equipotential Bonding :

Earthing ,

Earthing ensures that in the event of a fault, adequate fault current will flow causing rapid operation of a Circuit Protective Device (fuse, circuit breaker, or RCD) promptly disconnecting the supply. This limits the duration of any shock that one might receive, dramatically reducing the risk of serious injury or death :

For example, suppose a poorly positioned live wire in a washing machine becomes abraded by a sharp metal edge when the machine is running and this has the effect of making the casework of the machine "live". Since the case is connected (via its 13A plug) to mains earth, a high current will flow which will either blow the fuse in the plug and/or trip the RCD protecting the circuit :

During fault conditions, earthing may also reduce the voltage rise of anything earthed, which in addition to the limiting of the shock duration described above can also reduce the shock risk :

On general purpose socket circuits, the size of earthing conductors, and the circuit protective devices used are chosen to ensure that a fault is cleared within 0.4 seconds (or 0.2 seconds if the installation uses TT Earthing). For submains or higher power circuits feeding fixed equipment the time limit is 5 seconds (or 1 with TT) :

Main Equipotential Bonding ( 17th Edition , Main Protective Bonding Conductor )

Main bonding is the electrical interconnection of incoming (metallic) services (e.g. water, gas, and oil pipes) plus any extraneous conductive parts of a building (like the metal framework used in some buildings, or the central heating pipework), to the main electrical earth. This ensures that under fault conditions extraneous conductive parts, such as pipework, are not able to take on a dramatically different electrical potential to that of the installation's earth connection :

Supplementary bonding ( 17th Edition , Supplementary Protective bonding conductors’ / where required ,

Supplementary, or cross bonding is usually found in special locations containing a bath or shower. Unlike earthing it is not designed to clear a fault. What it does is electrically tie together all accessible conductive parts (pipes, taps, electrical appliances etc) that could under fault conditions introduce a dangerous potential (voltage) into the room :

For example suppose an electrically heated towel rail develops a fault which makes it electrically live. (Of course this also supposes that it is not earthed properly: which should never happen but the regulations adopt a belt and braces approach). Without bonding, such a fault would result in the towel rail being at mains voltage, while adjacent basin taps might offer a path to earth via the water pipework. This would be a very dangerous situation since touching both towel rail and a tap would expose one to a 230V potential difference across the arms and chest (including heart) probably causing severe injury or death :

However if the pipework feeding both hot and cold taps is bonded together with that of the earth of any electrical circuits supplying the room, then the towel rail fault will try to bring both taps up to mains voltage (230V). However touching both rail and tap at the same time exposes one to a potential difference of zero volts :

(Actually the bonding may fail to tie all elements together at exactly the same potential, but it is designed to limit any potential difference to 50V or less) :

The 17th Edition and Earthing & Equipotential Bonding

* Before an addition or alteration can be made to an existing installation it must be ascertained that the earthing and bonding arrangements comply with the current version of BS7671 and any existing equipment including the incoming supply is adequate for the proposed addition or alteration. 131.8
* Every installation must be provided with a main earthing terminal. 542.4.1
* The main earthing terminal, all bonding conductor connections and connections to an earth electrode must be permanently labelled 'Safety Electrical Connection - Do Not Remove'. 514.13.1
* Every joint and connection must be accessible. 543.3.3, 526.3
* All circuits must have a cpc that is terminated at each wiring point and at each accessory. 411.3.1.1

 

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* Rigid metal conduit and the metal sheath or armour of a cable can be used as a protective conductor. 543.2.2, 543.2.5
* Where rigid metal conduit or the metal sheath or armour of a cable is used as a protective conductor, a separate protective conductor must connect the earthing terminal of any accessories to the appropriate metal backbox. 543.2.7, 543.7.2.1

* All joints in metal conduit must be continuous. 543.3.6
* The cpc of flat cables must be sleeved when the cable sheath has been removed. 543.3.2
* Protective conductors must be identified by the colours green & yellow. 514.4.2 The single colour green is not permitted. 514.4.5
* In most domestic installations switches are not to be used with a protective conductor. 543.3.4
* All exposed-conductive-parts of a TN installation must be connected to the main earthing terminal. 411.4.2
* All extraneous conductive parts in an installation must be connected to the main earthing terminal by main protective bonding conductors. This applies to the metallic sheath of a telecommunication cable where permission from the owner of the cable must be obtained. 411.3.1.2
Main Earthing Conductor :
* The minimum csa of the main earthing conductor must be determined by the adibiatic equation or selected from Table 54.7 543.1.1. If the adibiatic equation is used, the minimum csa of the main earthing conductor must be 6mm 544.1.1. Table 54.7 suggests a 16mm main earthing conductor for phase conductors with a csa of up to 35mm.
* The csa of the main earthing conductor where PME conditions apply should be not less than that for a main protective bonding conductor (10mm) for the same installation 544.1.1. Invariably the electricity supplier will provide a 16mm main earthing conductor for a PME supply in a domestic property.
Main Protective Bonding Conductors :
* All extraneous conductive parts in an installation must be connected to the main earthing terminal by main protective bonding conductors. This applies to the metallic sheath of a telecommunications cable where permission from the owner of the cable must be obtained. 411.3.1.2
* For TN-S or TT systems the csa of main protective bonding conductors must be a minimum of 6mm and not be less than half the csa of the main earthing conductor. 544.1.1
* For a PME system the csa of the main bonding conductors must not be less than that given in Table 54.8 i.e. a 10mm protective bonding conductor for a neutral conductor of 35mm or less. 544.1.1
* For a service pipe, the main bonding conductor should be connected as near as possible to the point where the service enters the building. The connection must be before any branched pipework and on the consumers side of any meter. If possible the connection should be made within 600mm of the meter outlet. Where the meter is outside, the bonding connection should be made at the point of entry of the service into the building. 544.1.2

* Main bonding conductors should not be supported by the service pipes they are connected to. 543.3.1
* Where a main bonding conductor loops in and out to connect to an extraneous-conductive-part, the conductor should be unbroken at the connection. 528.3.3
* It is not necessary to run a main protective bonding conductor to an incoming service where the incoming service pipe and the consumers pipework are both made of plastic. If the incoming service pipe is made of plastic and the consumers pipework is made of metal it is recommended to main bond any metal pipework. OSG p29
Supplementary Bonding Conductors :
* Supplementary bonding is not required in a bath or shower room if all the extraneous conductive parts of the installation are connected to the main equipotential bonding. p6, 701.415.2
It is not generally required to supplementary bond the following :
* kitchen pipes, sinks, draining boards, metallic kitchen furniture, boiler pipes, metallic parts supplied by plastic pipes or metal pipes to hand basins or wc's ( excluding metal waste pipes in contact with earth ). OSG p31
Earth Electrodes : ( 542.2 – 542.2.1 )
* All of the following can be used as earth electrodes :
* Earth rods or pipes * Earth tapes or wires * Earth plates * Underground structural metalwork embedded in foundations * Welded metal reinforcement of concrete embedded in the Earth (excluding pre stressed concrete) * Lead sheaths & metal cable coverings provided the following conditions are met :
* a - the cable covering must be in effective contact with Earth
* b - the permission of the cable owner must be obtained
* c - the owner of the cable must be able to inform the owner of the installation of any changes to the cable which may affect it suitability as an earth electrode
* metal gas or water pipe must not be used as an earth electrode. 542.2.4

Why is inspection and testing necessary ?

Periodic inspection and testing is necessary because all electrical installations deteriorate due to a number of factors such as damage, wear, tear, corrosion, excessive electrical loading, ageing and environmental influences. Consequently legislation requires that electrical installations are maintained in a safe condition and therefore must be periodically inspected and tested.
Licensing authorities, public bodies, insurance companies, mortgage lenders and others may require periodic inspection and testing of electrical installations.
The law and inspection and testing

17% of all house fires are caused by electrical faults, due to lack of maintenance, poor and / or DIY work.

Existing domestic electrical installations are recommended to be inspected and tested at least once every 10 years or 5 years for rental properties. The purpose of this is to ensure the ongoing safety and efficiency of the installation, and to rectify any faults or degradation identified during the work.

It is also recommended that all in-service equipment is also regularly tested and inspected, labelled and records kept

Many house buyers may require a report regarding the age, condition and suitability of the electrical installation for mortgage and / or insurance purposes. This type of report can also be used as a bargaining point where the installation is found to be substandard.

 

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Introduction to the Changes : Apprentices

BS7671:2008 is the current national standard for all electrical work undertaken in
the United Kingdom. The first edition of BS7671 was published in 1992 and has
so far been amended six times. The 17th Edition is the result of a complete
review of the 16th Edition and aims to standardise the UK standards with the
Harmonised Documents (HD’s) produced by the European Committee for
Electrotechnical Standardisation (CENELEC).
A new informative note in the preface advises that publication of the
2008 edition of BS7671 does not automatically mean that installations complying
with previous editions are unsafe for continued use or need to be upgraded.
Numbering. The Regulation numbers are changed so as to be in line with
International Electrotechnical Commission (IEC) Numbers. This enables users to
readily relate UK regulations with European HDs and IEC regulations.
Fundamental Principles. Requirements are added for protection for persons and
livestock against injury, and property against damage caused by voltage
disturbances and electromagnetic influences.
Protection against electric shock – chapter 41.
• The chapter has been rewritten. Many regulations are worded differently but
the requirements are not significantly changed.
• The terms ‘Direct Contact’ and ‘Indirect Contact’ are no longer used. They are
replaced with Basic Protection and Fault Protection. ‘Basic protection’ is
protection against touching live parts. ‘Fault protection’ is protection against
receiving a shock from conductive parts that have become live due to a
breakdown of insulation or damage to equipment.
• Socket outlets rated not exceeding 20 A and intended for general use by
ordinary persons must be protected with 30 mA RCDs. This means that
general purpose sockets in domestic and similar properties must have
RCD protection.
• External sockets rated not exceeding 32 A must also have 30 mA
RCD protection.
• Maximum permitted earth loop impedance – Zs values have been adjusted,
based on 230V nominal and this has slightly reduced these, for example for
32amp type ‘B’ MCB protection the maximum permitted is 1.44ohms and was
previously 1.5ohms.
Selection and erection of wiring systems – chapter 52.
• An important new regulation that particularly affects domestic and similar
installations, requires cables that are buried less than 50mm into a wall or
partition and are not enclosed in earthed metallic covering or have mechanical
protection capable of resisting nails or screws to be protected by a 30 mA
RCD as well as being installed in the ‘safe zones’ created by the position of
accessories etc. as previously permitted.
• Similarly, irrespective of depth of cable, cables that are installed in metal framed
walls require 30 mA RCD protection if not otherwise protected by earthed
metallic covering.
• The above requirements do not apply to installations that are under the control
of skilled or instructed persons, such as office buildings, large retail outlets and
industrial premises.
• Maximum permitted volt drop where supplied directly from a public
distribution system is now 3% for lighting and 5% for all other applications.

Part P of the Building Regulations

Part P came into effect in England and Wales on the 1st January 2005. It is now a legal requirement for all work on fixed electrical installations in dwellings and associated buildings to comply with relevant standards. The relevant UK standard is BS 7671: 2008, 'Requirements for electrical installations' (The IEE Wiring Regulations 17th Edition). BS 7671 covers requirements for design, installation, inspection, testing, verification and certification.

To what types of electrical work does Part P apply?
• In a dwelling
•
• In the common parts of buildings serving one or more dwellings, but excluding power supplies to lifts
•
• In a building that receives its electricity from a source located within or shared with a dwelling, and
•
• In a garden or in or on land associate with a building where the electricity supply is from a source located within or shared with a dwelling
•

The term dwelling includes houses, maisonettes and flats. It also apply to electrical installations in business premises that share an electricity supply with dwellings, such as shops and public houses with a flat above.

The common parts of buildings includes access areas in blocks of flats such as hallways and shared amenities in blocks of flats such as laundries and gymnasiums.

Part P applies to electrical installations located in outbuildings such as detached garages, sheds and greenhouses.

Part P applies to parts of electrical installations located on land around dwellings such as garden lighting.

Part P applies to electrical installations that operate at voltages not exceeding 1000 V a.c.

Notifiable work includes new installations, house re-wires, and the installation

of new circuits. Notifiable work also includes additions to existing circuits in kitchens, bathrooms, outdoors and in other special locations. (See below ).
Will all electrical work need Building Regulations approval?
No. In general, notification will need to be given to, or full plans deposited with, a building control body only if the work is major involving one or more complete new circuits, and is not being carried out by an electrical contractor registered with an authorised competent person self-certification scheme.
What types of electrical work are 'non-notifiable'?

The following types of work are non-notifiable:
• Replacing accessories such as socket-outlets, control switches and ceiling roses
•
• Replacing the cable for a single circuit only, where damaged, for example, by fire, rodent or impact (note a)
•
• Re-fixing or replacing the enclosures of existing installation components (note b)
•
• Providing mechanical protection to existing fixed installations (note c)
•
• Work that is not in a kitchen or special location and does not involve a special installation (note d) and consists of:
•
• Adding lighting points (light fittings and switches) to an existing circuit (note e)
•
• Adding socket-outlets and fused spurs to an existing ring or radial circuit (note e)
•
• Installing or upgrading main or supplementary equipotential bonding (note f)
•

Notes:

(a) On condition that the replacement cable has the same current-carrying capacity, follows the same route and does not serve more than one sub-circuit through a distribution board

(b) If the circuit's protective measures are unaffected

(c) If the circuit's protective measures and current-carrying capacity of conductors are unaffected by increased thermal insulation

(d) Special locations and installations are listed below

(e) Only if the existing circuit protective device is suitable and provides protection for the modified circuit, and other relevant safety provisions are satisfactory

(f) Such work shall comply with other applicable legislation, such as the Gas Safety (Installation and Use) Regulations
Special locations and installations
• Locations containing a bath tub or shower basin
•
• Swimming pools or paddling pools
•
• Hot air saunas
•
• Electric floor or ceiling heating systems
•
• Garden lighting or power installations
•
• Solar photovoltaic (PV) power supply systems
•
• Small scale generators such as microCHP
•
• Extra-low voltage lighting installations, other than pre-assembled, CE-marked lighting sets
•

What are competent person self-certification schemes?

Electrical contractors who register with a competent person self-certification scheme will be able to self-certify compliance with the Building Regulations whenever they carry out 'notifiable' work. Persons who are not registered with a self-certification scheme - including DIYers - will need to notify or submit plans to a building control body, unless the work is non-notifiable as described above.

How many electrical self-certification schemes have been approved?

On the recommendation of BRAC (the Building Regulations Advisory Committee), the Government has approved schemes to be operated by:
• BRE Certification Limited
•
• BSI - British Standards Institution
•
• ELECSA Limited
•
• NAPIT Certification Ltd
•
• NICEIC Certification Services Limited
•

 

[amberleaf]

With a TT- Function ,
a Test Current of 15mA or less is applied between Line – Earth ,
It enable Loop Measurement without Tripping most RCDs 30mA : * ( your also checking the sensitivity of the RCD ) -&- 3291-10

RCD Test can be Selected :
Selector , from Either the Positive ( Oº ) or from ,
The Negative ( 180º ) half-Cycle of Voltage ,
At Both Polarity Test Minimum ( best ) and Maximum ( Worst ) Trip Times :

For TN- systems the Earth Fault Loop Impedance is the sum of the following Impedances :
Impedance of the power transformer secondary winding :
Impedance of the phase conductor from the power transformer to the location of the fault.:
Impedance of the protective conductor from the fault location to the power transformer :


If an electrical installation is protected by over-current protective devices including circuit breakers or fuses,
the earth Loop Impedance should be Measured In the event of a fault the earth fault Loop Impedance should be
low enough (and the prospective fault current high enough) to allow automatic disconnection of the electrical supply by the
circuit protection device within a prescribed time interval Every circuit must be tested to ensure that the earth fault Loop Impedance value does Not exceed that specified or appropriate for the over-current protective device installed in the circuit :

Tester takes a current from the supply and measures the difference between the unloaded and loaded supply voltages. From this
difference it is possible to calculate the Loop résistance
For a TT system the earth fault Loop Impedance is the sum of the following impedances
▲ Impedance of the power transformer secondary winding
▲ Impedance of the phase conductor resistance from the power transformer to the location of the fault
▲ The Impedance of the protective conductor from the fault location to the earth system
▲ Resistance of the local earth system (R).
▲ Resistance of the power transformer earth system (Re)

The figure below shows in marked line the Fault Loop Impedance for TT system.
When the protective device is a residual device ( RCD ), Ia is the rated residual operating current I∆n . For example in a TT system protected by an RCD the maximum RA values are as follows:

Rated residual
Operating ………. 10 ………. 30 ………. 100 ………. 300 ………. 500 ………. 1000
current IΔn mA
Ra (at 50V) Ω …. 50000Ω …. 1667Ω …... 500Ω …… 167Ω ………100Ω ………. 50Ω

For this example the maximum value is 1667Ω , the Loop tester
reads 12.74Ω and consequently the condition RA is 50 / Ia is met. It also important to test the operation of the RCD using a
dedicated RCD tester in accordance with the international standard IEC60364 for a TN system :

The following condition shall be fulfilled for each circuit Zs – Uo / Ia where Zs is the earth fault Loop Impedance voltage is the
nominal voltage between phase and earth and ( Ia ) is the current that causes the automatic disconnection of the protective device
within the time stated in the following table :

Note:
▲When the protective device is a residual current device( RCD ),
Ia is the rated residual operating current I∆n , For instance in a TN system with a nominal mains voltage of
Uo = 230V protected by type gG fuses the ( Ia ) and maximum Zs values could be :

Principles of the measurement of line :
Impedance and prospective short circuit current Line Impedance on a single phase system is the Impedance measured between phase and neutral terminals. Measurement principles for line impedance are exactly the same as for earth fault Loop impedance measurement with the exception that the measurement is carried out between phase and neutral :

The protective short circuit or fault current at any point within an electrical installation is the current that would flow in the
circuit if no circuit protection operated and a complete (very low impedance ) short circuit occurred
The value of this fault current is determined by the supply voltage and the impedance of the path taken by the fault current
Measurement of prospective short circuit current can be used to check that the protective devices within the system will operate
within safety limits and in accordance with the safe design of the installation. The breaking current capacity of any installed
protective device should be always higher than the prospective short circuit current :

If the prospective fault current is measured , its value must be higher than the ( Ia ) value of the protective device concerned

* The maximum value of Zs for this example is 2.70Ω (16 amp gG fuse, 0.4 seconds). The Loop tester reads 1.14Ω and consequently
the condition Zs Uo / Ia is met :

Accordance with the International Standard IEC 60364 , for a TT system the following condition shall be fulfilled for each circuit
RA must be 50 / Ia
Where ;
RA is the sum of the resistances of the local earth system :
R and the protective conductor connecting it to the exposed :
Conductor part. 50V is the maximum voltage limit ( it May be 25V in certain circumstances ).
( Ia ) is the value of current that causes automatic disconnection : of the protective device within 0.1 seconds

Principles of RCD Measurement :
The RCD tester is connected between phase and protective on the load side of the RCD after disconnecting the load.
A precisely measured current for a carefully timed period is drawn from the phase and returns via the earth, thus tripping the
device. The instrument measures and displays the exact time taken for the circuit to be opened ,
An RCD is a switching device designed for breaking currents when the residual current attains a specific value It works on the
basis of current difference between phase currents flowing to different loads and returning current flowing through the neutral
conductor (for a single-phase installation). In the case where the current difference is higher than the RCD tripping current, the
device will trip and disconnect the supply from the current There are two parameters for RCDs; the first due to the shape
of the residual current wave form (types AC and A) and the second due to the tripping time (types G and S). A typical RCD is AC-G.
▲ RCD type AC will trip when presented with residual sinusoidal alternating currents whether applied suddenly or slowly
rising. This type is the most frequently used on electrical installations :
▲ RCD type A will trip when presented with residual sinusoidal alternating currents (similar to type AC) and residual pulsating direct currents (DC) whether suddenly applied or slowly rising. This type of RCD is not commonly used at present, however, it is
increasing in popularity and is required by the local regulations in some countries
▲ RCD type G. In this case G stands for general type (without trip-out time delay) and is for general use and applications
▲ RCD type S where S stands for selective type (with trip- out time delay).This type of RCD is specifically designed for


Auto Ramp : Check your RCD settings , 1 x / 5 x ,
The RCD should trip. Check Trip Out Current.
(1) Press the 0°/180°switch to change the phase and repeat step

Heres the Good New,s Chaps , am doing my 2392-10 on Friday 23/ 10/ 09
Am OFF the Air for One Week , I’ve left you some things to be going on with , PS kicking A--- Amberleaf
am in Manchester ,
PS, this could be a 6-pack ? on Friday

 

[amberleaf]

17TH Edition , Questions & Answers for Examination 2382-10 Requirements for
1. The external influence code ACM requires IP rated equipment to
a. IPX4
b. IPX1
c. IPO
d. IPX2

Electrical Installations



2. AS 7671 is a
a. document designed solely for the use of electricians
I. legal document used in a court of law
c. Bon statutory document
d. statutory document

3. The fundamental principles of BS7671 state that persons and livestock shall be protected against injury as a
consequence of over voltages originating from
a. motors running
I. the operation of circuit breakers
c. atmospheric events
d. voltage recovery

4. The fundamental principles of BS 7671 covering the protection against voltage disturbances etc., states that the
installation shall have an adequate level of immunity against
a. the weather
b. electromagnetic disturbances
c. voltage loss
d. vibration

5. What is the maximum As for a 10A type C circuit breaker protecting a standard discharge type lighting circuit?
a. 1.15 Ohms
I. 2.30Ohms
c. 1.44Ohms
d. 1.92Ohms

6. A double insulated hand held electric drilling machine is known as
a. class II equipment
b. a DeWalt
c. class HI equipment
d. class I equipment

7. An electrical installation certificate should be signed by
a. the local authority
b. a competent person
c. the customer
d. the REC

8. When considering external influences, the code AD4 requires IP rated equipment to
a. IPXO
b. IPX1
c. IPX4
d. IPX5

9. The external influence code AD1 requires IP rated equipment to
a. IPX4
b. IPX1
c. IPXO
d. IPX2

10. When considering external influences, the code AA5 relates to the ambient temperature range
a. -5°C to +45°C
b. -65°C to +5°C
c. +5°C to +40°C
d. -25°C to 0°C


11. When considering external influences, the code AA1 relates to the ambient temperature range
a. -5°C to +45°C
b. -60°C to +5°C
c. +5°C to +40°C
d. -25°C to 0°C

12. Electrical installations shall be divided into circuits to
a. allow easier access to the installation
b. allow more even distribution of power
c. allow for expansion without changing the maximum demand
d. reduce electromagnetic interference

13. One method of determining the external loop impedance is by taking a reading at
a. the origin of supply
b. the supply and furthest outlet
c. the supply and subtracting the values of R1 + R2
d. the furthest outlet from the supply origin

14. The maximum disconnection time for a 230V a.c. final circuit not exceeding 32 amps, with a TT supply is
a. 3s
b. 0.2s
c. 0.5s
d. 5ms

15. The maximum Zs for a 16A Type B circuit breaker protecting a fixed appliance is
a. 1.87 Ohm
b. 0.87Ohm
c. 2.40Ohm
d. 2.87Ohm

16. Undervottage protection is required when the restoration of power may cause
a. accidental RCD tripping
b. unexpected stalling of the motor
c. overload activation
d. unexpected start-up of the machinery

17, A device which cuts off all or part of an installation from every source of electrical energy provides
a. emergency switching
b. isolatior
c. a fireman's switch
d. partial disconnection

18. For a 32A Type B circuit breaker protecting a standard final ring circuit, the maximum Zs would be
a. 0.70 Ohm
b. 0.30 Ohm
c. 1.44 Ohm
d. 0.20 Ohm

19. In a TT installation, distribution circuits must satisfy a disconnection time of
a. 5s

b. 1s
c. 0.6s
d. 0.2s

20. A residual current device (RCD) works by
a. a magnetic device operating in the event of a fault between Live and earth «-> CORRECT ANSWER
b. a magnetic device operating in the event of a fault between neutral and earth
c. a thin element operating in the event of a fault between neutral and earth
d. a thin element operating in the event of a fault between live and earth

21. A RCBO offers protection against
a. short circuit current
b. short circuit and earth fault current
c. short circuit and overload current
d. basic contact

22. Protective measures against electric shock can be achieved by automatic disconnection of the supply and in systems additional protection by means of an red shall be provided for
a. mobile equipment with a current rating exceeding 32 A
b. mobile equipment with a current not exceeding 22 A
c. socket outlets with a rated current exceeding 20 A
d. socket outlets with a rated current not exceeding 20 A
systems additional protection by means of an rcd shall be provided for

23. Protective measures against electric shock can be achieved by automatic disconnection of the supply and in systems additional protection by means of an red shall be provided for
a. socket outlets with a rated current exceeding 20 A
b. socket outlets with a rated current not exceeding 13 A
c. mobile equipment with a current rating not exceeding 32 A
d. mobile equipment with a current rating exceeding 32 A

24. In a.c. systems in the event of the failure of basic protection, additional protection may be provided by
a. supplementary bonding
b. a time delay 100mA RCD
c. an RCD with an operating current not exceeding 30mA
d. electrical separation

25. If a fault occurs in the HV system, and a magnitude of fault voltage of 430 volts occurs between exposed conductive
parts and earth on the LV installation. What is the maximum tolerable duration of the fault?
a. 10 ms
b. 100 ms
c. 200 ms
d. 300 ms

26. If a Line conductor of an IT system is earthed accidentally, the insulation and components rated for the Line to
Neutral voltage can be temporarily stressed with a higher voltage. What value can this stress voltage reach up to?
a. U=V3 U0
b. U=3U0
c. U=V U0
d. U=U0

27. Nuisance tripping from a large transformer installation can be prevented by
a. the use of an RCD
b. the use of a C type MCB
c. the use of a B type MCB
d. the use of a D type MCB

28. In order to reduce the effects of eddy currents when conductors are drawn through a steel conduit system, they
should be arranged so that
a. they are terminated in the correct phase sequence
b. each conductor of an individual circuit takes approximately the same current
c. they are physically separated from the conductors of other circuits within the conduit
d. they are not individually surrounded by the ferrous material -> CORRECT ANSWER

29. If a cable is buried in a wall less than 50mm depth and is not protected by metallic enclosures, the additional
protection required is
a. RCD protection -
b. MCB protection
c. supplementary bonding
d. external notification of cable routes

30. At which one of the following terminations would a warning notice NOT need to be attached
a. a copper water pipe
b. a bonded gas pipe
c. an earthing terminal within a consumer unit
d. an earth electrode

31. When determining design current, the correction factor that is applied to a BS3036 rewirable fuse is
a. 0.752
b. 0.527
c. 0.725
d. 1.725

32. A BS1361 protective device is also known as a
a. circuit breaker
b. cartridge fuse
c. RCD
d. semi enclosed rewirable fuse

33. An installation protected by an RCD shall have a fixed notice stating
a. the test button should be pressed occasionally
b. the test button should be pressed monthly
c. the test button should be pressed quarterly
d. the test button should be pressed at 6 monthly intervals

34. When insulated a PEN conductor shall be identified with
a. blue insulation along its length
b. green insulation and blue markings at the termination
c. green and yellow insulation and blue markings at the termination
d. green and yellow insulation along its length

35. Outdoor lighting does NOT involve
a. shelters
b. festoon lighting
c. road trafic signals
d. floodlighting

36. Where it is necessary to install cables within a wall consisting of a metal construction, the circuit should
a. adequately bond the studwork
b. be RCD protected
c. be MCB protected
d. be sheathed in metallic conduit

37. Where it is necessary to limit the consequences of the risk of fire due to fault currents, an RCD
a. shall be installed at the end of the circuit to be protected

 

[amberleaf]

b. shall be installed at the origin of the circuit to be protected
c. is used to switch off the line conductor in the event of a faun
d. is used to switch off the neutral conductor in the event of a fault

38. In Great Britain the use of Combined protective and neutral (PEN) conductors is prohibited in consumers installations by which regulations?
a. The Electricity at Work Regulations 1989
b. The Supply of Machinery (Safety) Regulations 1992
c. The IEE Wiring Regulations
d. The Electricity Safety, Quality and Continuity Regulations 2002

39. In Great Britain the use of Combined protective and neutral (PEN) conductors is prohibited in consumers installations. One of the exceptions from this is
a. where the supply is feeding an agricultural installation
b. where the installation is supplied by a privately owned transformer which has a metallic connection with the distributors
network
c. where the supply is obtained from a private generating plant
d. where the supply is feeding a swimming pool

40. Where a generating set is used as an additional source of supply in parallel with other sources, it shall be instated
a. on the supply side of all the protective devices for the final circuits of the installation with a number of additional
requirements
b. on the supply side of all the protective devices for the final circuits of the installation with no additional requirements ~>
c. on the load side of all the protective devices for the final circuits of the installation with no additional requirements
d. on the load side of all the protective devices to the final circuit which must be connected by plug and socket

41. Regarding auxiliary supplies to safety services, the maximum changeover time refers to
a. how long the safety source can supply the rated power output to the safety service
b. the frequency (in cycles per second) of the auxiliary supply feeding the safety service
c. how often maintenance has to be carried out on the auxiliary supply
d. the time It takes for the safety source to supply the power to the safety service, after the loss of the main power supply

42. The minimum value of insulation resistance test performed on a PELV installation is
a. 10.0 MOhm
b. 2.0 MOhm
c. 0.3 MOhm
d. 0.5 MOhm

43. The minumum value of insulation resistance test performed on a SELV installation is
a. 99.0 MOhm
b. 2.0 MOhm
c. 0.3 MOhm
d. 0.5 MOhm

44. During the initial verification of an installation, which of the following forms part of the checklist?
a. maximum demand and diversity
b. Design briefs
c. contractors notes
d. presence of diagrams and instructions

45. An earth fault loop impedance test performed on a final ring circuit will record
a. the external loop impedance
b. the resistance of the line and protective conductors and external loop impedance
c. the resistance of the line and protective conductors
d. the protective conductor resistance

46. A polarity test would be conducted to verify
a. every fuse and single pole device is connected in the line conductor only -
b. there is sufficiently low resistance to operate the protective device within its limits
c. there is sufficient circuit protection
d. there is no breakdown of the conductor insulation

47. The minimum value of insulation resistance of a PELV circuit is
a. 0.5 MOhm
b. 1MOhm
c. 1.5 MOhm
d. 5MOhm

48. Within an agricultural installation, bonding conductors can be
a. 6.0mm2 aluminium conductors
b. 4.0mm2 aluminium conductors
c. 4.0mm2 copper conductors
d. 5.0mm2 copper conductors

49. Self supported suspension cables within agricultural situations should be
a. at a height of a least 2m
b. at a height of a least 4m
c. at a height of a least 6m
d. at a height of a least 10m

50. If SELV or PELV is used within agricultural premises, barriers or enclosures must conform to at least
a. IP4X
b. IPXXB
c. IPX4
d. IP67

51. Within zone 2 of an outdoor swimming baths where no water jets are used, installed electrical equipment should be rated
a. IPX4
b. IP2X
c. IPXXB
d. 1PX8

52. In an area containing a bath or a shower, socket outlets must be installed
a. 3m horizontally from zone 1
b. 3m horizontally from zone 0
c. 3m horizontally from zone 2
d. within zone 2 but outside zone 1

53. Where contact with skin or footwear is likely, the floor temperature of an underfloor heating installation should be limited to
a. 20°C
b. 35°C •
c. 40°C
d. 70°C


54. A mobile unit should have a connection between the
a. live and neutral
b. neutral and earth
c. vehicle chassis and main bonding terminal
d. battery terminals and supply

55. On the d.c. side of a PV power supply system, the type of insulation that is preferable is
a. Class II-
b. Class I
C XLPE

d. 1000v VDS

56. In marina installations that are NOT in an area subject to vehicle movement, overhead distribution cables shaft be installed at a height of
a. 5.5m
b. 4.5m
c. 6.5m
d. 3.5m

57. In areas that are not subject to vehicle movement on a caravan site, overhead distribution cables shall be installed at a heigth of
a. 6m
b. 3.5m
c. 5m
d. 10m



58. BS 6004 relates to
a. emergency lighting
b. electrical cables
c. 13A plug cartridge fuses
d. RCDs

59. BS 5266 relates to
a. emergency lighting -
b. electrical cables
c. 13A plug cartridge fuses
d. 13A plugs

60. The correction factor for three multicore cables installed in single layer fashion on a wail is
a. 0.75
b. 0.85
c. 0.79
d. 0.99


ANSWERS

1-a 2-c 3-c 4-b 5-b 6-a 7-b 8-c 9-c 10-c 11-b 12-d 13-a 14-b 15-d 16-d 17-b 18-c 19-b

20-a 21-b 22-d 23-c 24-c 25-d 26-a 27-d 28-d 29-a 30-c 31-c 32-b 33-c 34-c 35-b 36-b

37-b 38-d 39-c 40-b 41-d 42-d 43-d 44-d 45-b 46-a 47-a 48-c 49-c 50-b 51-a 52-a 53-b

54-c 55-a 56-d 57-b 58-b 59-a 60-c
________________________________________

17th Edition stuff , Part 4 -
Protection for Safety :

Part 4 is reorganised with subject matter more closely grouped eg basic requirements and application requirements are now in the same chapter.
Part 4 has also a number of important changes.
Protection against direct contact has been replaced by “basic protection” which is defined as:- protection against electric shock under fault free conditions.
Protection against indirect contact has been replaced by “fault protection” which is defined as:- protection against electric shock under single fault conditions.
EEBADS is now an out of date term referring only to fault protection measures and this is now replaced by ADS:- Automatic Disconnection of Supply, which is a protective measure including both basic and fault protection.
Table 41A – Maximum disconnection times, has been extended and modified. Now replaced by table 41.1 this new table includes final TN and for the first time TT circuits. Disconnection times for circuits not exceeding 32A are tabulated for a range of ac and dc nominal line voltages
E.g.:
for a 230V I6A TN circuit t = 0.4s
for a 230V 16A TT circuit t = 0.2s
for final circuits exceeding 32A:- for a 230V TN circuit, t = 5s : max for a 230V TT circuit t = 1s max :

The terms fixed and non fixed equipment have been removed and no longer apply e.g. for previous fixed equipment in a TN circuit the value of 5s no longer applies and is now covered in table 41.1 as 0.4s or for circuits exceeding 32A, 5s.
As well as maximum disconnection times for TT systems being introduced into BS 7671 where an RCD is used for earth fault protection in a TT system an additional condition must be met. This is that RA x I∆n ≤ 50V (section 411.5.3).

 

[amberleaf]

2392-10 : just off the press this is the New Sh—there hitting you with ,


(42) Prospective Short Circuit Current is Measured at the Supply with the Main Earthing Conductor :
(a) Connected to the Main Earth Terminal :
(b) Connected to the Neutral Supply :
(c) Disconnected from the Main Earth Terminal : *****
(d) Connected to the Line Supply :

Measurement of Prospective Short Circuit Current :
CCU :
Note : the Neutral & Earth Probes are Connected to the Natural Terminal ( Line by is self )
Note : Not on the ( MET ) Main Earthing Terminal ( Earth Connection Block :

(41) Prospective Earth Fault Current ( PEFC ) is Measured between :
(a) Line & Neutral :
(b) Line & Earth : *****
(c) Neutral & Earth :
(d) R1 & R2
Measurement of Prospective Earth Fault Current :
CCU :
Note : the Neutral Probe (N) Only : the Line Probe ( L ) Only :
Note : Earth Probe : on the ( Earth Connection Block : ( MET )

(40) Prospective Short Circuit Current ( PSCC ) is Measured between :
(a) Line & Neutral : *****
(b) Line & Earth :
(c) Neutral & Earth :
(d) R1 & R2

(0)Measurement of External Loop Impedance : ( Ze )
CCU :
Note : the main Earth is Disconnected from main bonding conductors and Circuit Protective conductors for this Test ,
Note : Main Switch in “ OFF “ Position :
Note : the Neutral Probe (N) Only : the Line Probe ( L ) Only :
Note : Earth Disconnected from the ( MET ) Main Earthing Terminal

(37) RCD tests should include :
(a) Half times /no trip , 1 times 40mS , 5 times / 0.45 ,
(b) Half times / 40mS , I times no trip , 5 times / 300ms ,
(c) Half times / no trip , I times 300mS , 5 times / 40mS **** ( am basing them on BS-EN - )
(d) Half times / 0.45 , I times 30mS , 5 times / 300mS ,

(31) When checking Polarity with test probes the voltage indication on a single phase socket outlet should be :
(a) L-N 230V , L-E 230V , N-E , 230V
(b) L-N 230V , L-E 0V , N-E , 230V
(c) L-N 0V , L-E 230V , N-E , 0V ,
(d) L-N 230V , L-E 230V , N-E , 0V , *****

( 47) An Electrical Installation Certificate consists of : ( Remember this One a Must ) ↔↔↔↔↔↔↔↔↔↔↔↔↔
(a) A two page Certificate :
(b) A two page Certificate and Schedule of Inspections :
(c) A two page Certificate and Schedule of Test Results :
(d) A two page Certificate, A Schedule of Inspections and a Schedule of Test Results :

(48) The Electrical Certificate required to be completed for a domestic shower circuit would be : ( Remember this One a Must ) ↔↔↔
(a) A Minor Works Electrical Installation Certificate :
(b) A Minor Works Electrical Installation Certificate and a Schedule of Test Results :
(c) A Minor Works Electrical Installation Certificate and a Schedule of Inspections and a Schedule of Test Results : *****
(d) No Certification Required :

( 47) ( D ) Ops

(49) Volt drop in a cable will :
(a) Increase with Increase in Length : *****
(b) Decrease with increase in Length :
(c) Not affected by increase in Length :
(d) Increase with a reduction in length :

(44) Voltage drop can be evaluated by using which one of the following test values :
(a) External Loop Impedance (Ze ) :
(b) Final Circuit earth Fault loop Impedance (Zs ) : *****
(c) Insulation Résistance :
(d) RCD tripping times :

2392-10 : Certificate in Fundamental Inspection and Initial Verification of Electrical Installations

(1) An initial verification is carried out to ensure that :
(a) All fixed equipment , parts and material are erected correctly to British Standards : *****
(b) No claim can be made for poor workmanship :
(c) A certificate is issued to the tenant of the property :
(d) The building insurance policy cast is kept to a minimum :

(2) Three items of information required for the initial inspection are :
(a) Maximum demand , type of earthing and supply characteristics : *****
(b) Cost of work, time taken and number of electricians :
(c) Serial number of instrument , schedule of test results , order number :
(d) Estimated time , start time and total hours taken :

(3) Three statutory and non statutory most relevant guidance materials for initial verification :
(a) COSHH regs , CDM regs , and PUWER regs , :
(b) Working at Height regs , and Working in Confined Spaces Act :
(c) Health and Safety Policy , Liability insurance and building insurance :
(d) EAWR 1989 , BS-7671:2008 , and IEE guidance notes 3 : *****

(4) Three locations and associated equipment requiring specific guidance material would be :
(a) Bedroom ,Lounge and Garage :
(b) Roofs , Cellars and Lofts :
(c) Explosive atmospheres , combustible dust and open cast mines : ( Mac two Answers on sheet C / D ) ???????? Help
(d) Offices , workrooms and classrooms :

(5) Some of the essential and optional information required on the Electrical Installation Certificate and Minor Electrical Installation Work Certificate is :
(a) Number of rooms , type of lighting , outdoor supplies :
(b) Floor area , separate building , number of floors ,
(c) Means of earthing , main protective conductors and supply characteristics : *****
(d) Name of sub-contractor , invoice , contact number :

(6) Two human senses that may be employed during the initial verification are :
(a) Thought and speech :
(b) Movement and pain :
(c) Gut feeling and taste :
(d) Sight and touch : *****

(7) Two main items to be checked for given systems and locations are :
(a) Light levels and stroboscopic effect :
(b) Number of appliance and Pat test labelling :
(c) Connection of conductors and cable selection : *****
(d) Empty premises or tenanted :

(8) Two requirements of the EAWR 1989 for safe inspection and testing are :
(a) Excess current protection and means of isolation : *****
(b) Two inspectors are required and one person under supervision :
(c) Presence of tenant and building inspector during verification :
(d) Spare instrument batteries and spare test leads :

(9) Instruments should be in accordance with :
(a) HSG 141 ,
(b) GS-38 , *****
(c) BS-7671 ,
(d) IEE Guidance Note 3 ,

(10) The correct Instruments or settings required to carry out domestic installation testing are ,
(a) Multimeter , Ammeter , Voltmeter and Watt meter ,
(b) Low insulation tester , light meter , power meter ,
(c) Pipe locator , cable finder , fuse checker and buzzer ,
(d) Continuity , insulation , loop impedance and RCD , ***** GN-3

(11) The first three tests to carry out on an initial verification are :
(a) Verification of switch operation , fuse test and lamp test ,
(b) Continuity of protective conductors , continuity of ring and insulation résistance , ***** GN-3
(c) Verification of voltage drop , functional testing of polarity ,
(d) Electrical separation , earth electrode test and phase sequence ,

(12) The four earthing arrangements in a domestic installation are ,
(a) Cross bond , main earth , earth electrode and supply cable earth ,
(b) Protective conductors in lighting , socket outlets , cooker and shower ,
(c) Bonding conductors to Gas , Water , Central heating and kitchen sink ,
(d) Main earth , main bonding , circuit protective conductors and supplementary bonding , *****

(13) Continuity of protective conductors gives a reading of ,
(a) R1 + Rn ,
(b) Ze + Zs ,
(c) R1 + R2 , ***** ( remember they are not asking you about little r1 + r2 , End to End
(d) r1 + r2 ,

(14) Increasing conductor length and decreasing conductor cross sectional area , ( CSA )
(a) Increases résistance , ***** Remember this one ,
(b) Decreases résistance ,
(c) Has no effect on résistance ,
(d) Causes the résistance value to remain the same due to both changes ,

(15) An increase in ambient temperature would cause the résistance of a conductor to ,
(a) Increase ,
(b) Decrease ,
(c) Vary ,
(d) Remain the same ,

(16) Connecting conductors’ in parallel would ,
(a) Reduce the overall value of résistance , *****
(b) Have no effect on the résistance compared to one conductor ,
(c) Double the résistance value of résistance ,
(d) Increase the overall value of résistance ,

(17) On a ring continuity test (R1 + R2 ) can be calculated by ,
(a) Adding line ( r1 ) and protective conductor ( r2 ) ,
(b) Subtracting ( r2 ) from ( r1 ) ,
(c) Adding ( r1 ) to ( r2 ) and dividing by ( 4 ) , **** ( Remember this if your doing your 2391-10 ) look back on these pages , it all there ,
(d) Adding ( r1 ) to ( r2 ) and multiplying by ( 4 ) ,

(18) Decreasing a conductor length with cause its résistance to ,
(a) Remain the same ,
(b) Vary ,
(c) Increase ,
(d) Decrease , *****

(19) Where cables are connected in parallel the overall insulation résistance ,
(a) Stay the same .
(b) Varies ,
(c) Increase ,
(d) Decreases ,

(20) Insulation résistance is measured in ,
(a) mΩ
(b) Ω
(c) KΩ
(d) MΩ

(21) Before carrying out an insulation résistance test consideration must be given to ,
(a) Client consultation , safety procedures and notices , *****
(b) Checking the results and verifying them ,
(c) The supply voltage and frequency ,
(d) Ze and PFC ,

(22) Before carrying out an insulation résistance test ,
(a) Carry out verification of voltage drop ,
(b) Ensure supply is switched on ,
(c) Contact local authority building control ,
(d) Safely isolate and consider electronic components and voltage sensitive equipment , *****

(23) When carrying out an insulation résistance test , tests should be between ,
(a) Live to Neutral and Live to Earth , ( Mac two Answers on sheet A / B ) ???????? Help ( Myself ( A ) Tutors for you ?
(b) Live to Live and Live to Earth ,
(c) Earth to Neutral and Earth to Earth ,
(d) Neutral to Neutral and Live to Earth ,

( A low resistance between phase and neutral conductors, or from live conductors to earth, will result in a leakage current. )

 

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(24) The required test voltage and minimum value of résistance for circuit above 50V to 500V is :
(a) 250v / 0.5mΩ ,
(b) 500v / 1MΩ , *****
(c) 250v / 1MΩ ,
(d) 500v / 0.5MΩ ,

(25) The insulation résistance test to verify separation between SELV circuits and other circuits should be ,
(a) 250v / 0.5mΩ ( table 61 regs ) *****
(b) 500v / 1MΩ
(c) 250v / 1MΩ
(d) 500v / 0.5MΩ

(26) A shower located in a room above a bath would be : ( regs 701.512.2 (ii ) in zone 1 – 2 : IPX4 , lighting bathroom ,
(a) In zone 0 , IP4X and not RCD protected ,
(b) In zone 1 , IPX4 and RCD protected , *****
(c) In zone 2 , IPX8 and not RCD protected ,
(d) In zone 0 , IPX8 and RCD protected ,
( anything that moves in bathroom RCD it 30mA ) 17th Edition ,
( Zone 1 : IPX4 , Zone 0 : IPX7 , Zone 2 : IPX4 , Electrical equipment exposed to water jets , e.g. IPX5 : ←←←

(27) The appropriate IP code for finger protection from contact with a Live terminal is ,
(a) IP2X , ***** ( how to remember Two Finger up , V )
(b) IP4X ,
(c) IPX2 ,
(d) IPX4 ,

(28) A polarity test is carried out to confirm ,
(a) RCD is in the Live side of the circuit ,
(b) Main double pole switch is in the Live side of the circuit ,
(c) Single pole switches , cable contact of Edison screw lampholders and fuses are in the Live side of the circuit , *****
(d) Double pole switches are in the Live side of the circuit ,

(29) Correct polarity of a final circuit can be confirmed during the ,
(a) Protective conductor continuity test ( R1 + R2 ) , *****
(b) Insulation résistance test ,
(c) External loop impedance test ,
(d) Protective fault current test ,

(30) Correct polarity is confirmed when supply is switched on to confirm ,
(a) Correct polarity of final circuit ,
(b) Correct polarity of final circuit and supply connections , *****
(c) Correct polarity of supply connections ,
(d) Correct polarity of portable equipment ,

(32 ) Earth electrodes’ can be tested using ,
(a) A voltmeter or ammeter ,
(b) A Insulation résistance tester or continuity tester ,
(c) An earth electrode or loop impedance tester , ***** ( Remember 2 Instrument’s Used , method 1 , method 2 , )
(d) An RCD tester or frequency meter ,

(33) When measuring earth electrodes’ using an earth fault loop impedance tester the tester should be connected ,
(a) To the furthest point ,
(b) To every socket outlet of the ring in turn ,
(c) To the installation supply with the main earthing conductor disconnected from the main earthing terminal , *****
(d) At mid point in a ring circuit ,

(34) A supply earthing arrangement which has a combined neutral and earth is a ,
(a) TN-S- system ,
(b) TN-C-S - system , ***** ( Look up in the regs , Definitions , p-33 )
(c) TT- system ,
(d) IT- system ,

(35) Earth fault loop impedance values for ( Zs ) is carried out ,
(a) At the supply ,
(b) At the first socket in a ring circuit and furthest lighting point in a lighting circuit ,
(c) At all consumer unit MCB outgoing terminals ,
(d) At all sockets in a ring circuit and furthest lighting point in a lighting circuit , *****

(36) A measured value of ( Zs ) can be compared with the maximum tabulated value by 0.8 ,
(a) Multiplying the tabulated value by 0.8 , ↔ ( Mac I could be wrong here I’ll stick my neck out ) Help !!!!!! A / D
(b) Multiplying the measured value by 0.8 ,
(c) Dividing the tabulated value by 0.8 ,
(d) Dividing the measured value by 0.8 ,

Ambient temperature at the time of test , and the maximum conductor operating temperature , both of which will have an effect
On conductor résistance , hence , the ( R1 + R2 ) could be greater at the time of fault than at the time of test ,
Our measured value of ( Zs ) must be corrected to allow for these possible increases in temperature occurring at a later date , this
Requires actually measuring the ambient temperature and applying factors in a formula ,
( which simply requires that the measured value of ( Zs ) does not exceed 0.8 of the appropriate tabulated value gives the 0.8 values of the tabulated loop impedance for direct comparison with measured values )
In effect , a loop impedance test places a Line / Earth Fault on the Installation ,
The value of ( Zs ) will have to be determined from measured values of ( Ze ) and ( R1 + R2 ) and the 0.8 rule applied ,

Note : Never Short out an RCD in Order to conduct this Test :
As a Loop Impedance test creates a high Earth Fault Current , albeit for a Short Space of time , some lower rated circuit breakers may operate , resulting in the same situation as with an RCD , and ( Zs )
Earth Fault Loop Path : Fault current , Exposed Conductive Path , TN-C-S ( Ze – 0.35Ω pen conductor ) TN-S ( Ze – 0.8Ω )

External Loop Impedance ( Ze )
The value of ( Ze ) is measured at the intake position on the supply side , and with all main protective bonding disconnected ,
Unless the Installation can be isolated from the supply , this test should not be carried out ,
As a potential shock risk will exist with the supply on and the main protective bonding disconnected ,

Additional protection RCD / RCBO operation :
Where RCDs / RCBOs are fitted it is essential they operate within set parameters , The RCD testers used are designed to do just this ,
Basic tests required are as follows :
(1) Set the Instrument to the rating of the RCD :
(2) Set the Instrument to half-rated trip :
(3) Operate the Instrument and the RCD , should “ Not trip “
(4) Set the Instrument to deliver the full rated tripping current of the RCD , ( I∆n )
(5) Operate the Instrument and the RCD , should trip out in the required time :
(6) For RCDs rated at 30mA or less set the Instrument to deliver ( x5 ) times the ratted current of the RCD , ( 5 I∆n )
(7) Operate the Instrument and the RCD , should trip out in ( 40mS )

( PS , I wont give up my day job )

(38) RCDs can be used for ,
(a) Overload protection of portable appliances ,
(b) Additional protection of socket outlets up to 20A , special locations’ and installations , *****
(c) Fault current protection of equipment and socket outlets rated above 32A
(d) Basic protection ,

(39) RCDs connected in series must have ,
(a) Delay operation facilities ,
(b) Indicator lamps of different colours ,
(c) One combined test button facility ,
(d) Discrimination between RCDs , *****

(43) Prospective fault current measurement ensures that ,
(a) Cables can carry the required load current ,
(b) The consumer unit main switch can be operated during a fault ,
(c) The over current protective devices at that point in the installation can disconnect the fault current , *****
(d) The main fuse will operate in the event of a fault ,

(45) The maximum permitted voltage drop to BS-7671:2008 for ,
(a) 4% lighting 4% other uses ,
(b) 9.2% lighting 4% other uses ,
(c) 2.5% lighting 4% other uses ,
(d) 3% lighting 5% other uses , ( Appendix 12 , p-358 ) *****

(46) The requirements for erection of electrical installations are given in ,
(a) Electricity at Work Regulations 1989 ,
(b) IEE On Site Guide ,
(c) Building Regulations ,
(d) BS-7671 :2008 , ***** ( regs chapter 52 : P-97 )

(50) Instruments used for electrical installation testing should be ,
(a) Calibrated on a regular basis , *****
(b) Exempt from calibration ,
(c) Calibrated after and initial verification ,
(d) When the batteries are dead ,

State the Recommended Sequence of Tests Covered by this Unit and the Reasons for that Sequence :

Sequence taken from BS-7671 : 2008 Part 6

………………….. Test …………………………………………….. Reason ………..
Continuity of protective conductors : R1 + R2 value , Metalwork & Effective IR testing
Continuity of Ring Final Circuit : R1 + R2 value , No Interconnected ring
Insulation Résistance : No Short-between Line , Neutral & Earth
SELV : No Connection between Low & Extra Low-Circuits
PELV No Connection between Low & Extra Low-Circuits
Electrical Separation : No Connection between Low & Extra Low-Circuits
Basic protection by barrier or Enclosure : No finger or other solid more than 1mm
Insulation / Impedance of Floors and Walls : Effectiveness of high Résistance / Impedance Location
Polarity : Switches , Fuses , breakers etc in live side of circuit
Earth Electrode Résistance : Resistive Contact of Electrode to Ground :
Earth Fault Loop Impedance : To meet final circuit disconnection time in event of fault :
Additional protection / RCD test : To ensue RCD operates in time in event of Fault or misuse :
Prospective Fault Current : To ensue protective devices can disconnect fault effectively :
Check of Phase Sequence : To ensue 3 Phase motors etc, rotate incorrect direction :
Functional Testing : To Test RCD test button , Switches , breakers , locks etc, operate
Verification of Volt Drop : To ensue voltage at load end is within required limits ,

 

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Insulation Resistance Testing: How and Why ? Our cousins Overseas : IEE :

How significant is insulation resistance testing ? Since 80% of electrical maintenance and testing involves evaluating insulation integrity, the answer is "very important." Electrical insulation starts to age as soon as it's made. And, aging deteriorates its performance. Harsh installation environments, especially those with temperature extremes and/or chemical contamination, cause further deterioration. As a result, personnel safety and power reliability can suffer. Obviously, it's important to identify this deterioration as quickly as possible so you can take the necessary corrective measures.
What is insulation resistance testing? Basically, you're applying a voltage (specifically a highly regulated, stabilized DC voltage) across a dielectric, measuring the amount of current flowing through that dielectric, and then calculating (using Ohm's Law) a resistance measurement. Let's clarify our use of the term "current." We're talking about leakage current. The resistance measurement is in megohms. You use this resistance measurement to evaluate insulation integrity.
Current flow through a dielectric may seem somewhat contradictory, but remember, no electrical insulation is perfect. So, some current will flow.
What's the purpose of insulation resistance testing? You can use it as:
• A quality control measure at the time a piece of electrical equipment is produced;
• An installation requirement to help ensure specifications are met and to verify proper hook up;
• A periodic preventive maintenance task; and
• A troubleshooting tool.
How do you perform an insulation resistance test? Generally, you connect two leads (positive and negative) across an insulation barrier. A third lead, which connects to a guard terminal, may or may not be available with your tester. If it is, you may or may not have to use it. This guard terminal acts as a shunt to remove the connected element from the measurement. In other words, it allows you to be selective in evaluating certain specific components in a large piece of electrical equipment.
Obviously, it's a good idea to have a basic familiarity with the item you're testing. Basically, you should know what is supposed to be insulated from what. The equipment you're testing will determine how you hook up your meghommeter.
After you make your connections, you apply the test voltage for 1 min. (This is a standard industry parameter that allows you to make relatively accurate comparisons of readings from past tests done by other technicians.)
During this interval, the resistance reading should drop or remain relatively steady. Larger insulation systems will show a steady decrease; smaller systems will remain steady because the capacitive and absorption currents drop to zero faster than on larger systems. After 1 min, you should read and record the resistance value.
When performing insulation resistance testing, you must maintain consistency. Why? Because electrical insulation will exhibit dynamic behaviour during the course of your test; whether the dielectric is "good" or "bad." To evaluate a number of test results on the same piece of equipment, you have to conduct the test the same way and under the relatively same environmental parameters, each and every time.
Your resistance measurement readings will also change with time. This is because electrical insulation materials exhibit capacitance and will charge during the course of the test. This can be somewhat frustrating to a novice. However, it becomes a useful tool to a seasoned technician.
As you gain more skills, you'll become familiar with this behaviour and be able to make maximum use of it in evaluating your test results. This is one factor that generates the continued popularity of analogue testers.
What affects insulation resistance readings? Insulation resistance is temperature-sensitive. When temperature increases, insulation resistance decreases, and vice versa. A common rule of thumb is insulation resistance changes by a factor of two for each 10 DegrC change. So, to compare new readings with previous ones, you'll have to correct your readings to some base temperature. For example, suppose you measured 100 megohms with an insulation temperature of 30 DegrC. A corrected measurement at 20 DegrC would be 200 megohms (100 megohms times two).
Also, "acceptable" values of insulation resistance depend upon the equipment you're testing. Historically, many field electricians use the somewhat arbitrary standard of 1 megohm per kV. The international Electrical Testing Association (NETA) specification Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems provides much more realistic and useful values.
Remember, compare your test readings with others taken on similar equipment.

The 17th Edition :

Limits this to : ( regs p-358 )
Voltage drop in Consumer’s Installations ,
The Voltage drop between the origin of an Installation and any load point should not be greater than the values in table 12A
Expressed with respect to the value of the nominal voltage of the Installation ,
The calculated Voltage drop should include any effect due to harmonic currents :

3% for lighting ,
5% for Other Uses ,
3% of 230 = 6.9v
3 x 230 ÷ 100 = 6.9v
5% of 230v = 11.5v
5 x 230 ÷ 100 = 11.5v

6% & 8% respectively are permitted for private supplies ,

Ring Final Circuit : GN-3 ( Dead Test ) 2392-10
Instrument : Set : on Ohms –

Under : “ Schedule of Test Results “ Circuit Loop Impedance Ω : ( Ring Final Circuits , Only Measured End to End ,

Line / Line : Little : r1 = 0.43Ω ( Measured End to End ) ↔ Big Copper Lower Résistance )
Neutral / Neutral : Little : r n = 0.42Ω ( Measured End to End ) ↔ Big Copper Lower Résistance )
Earth – Earth : Little : r2 = 0.73Ω ( Measured End to End ) ↔ Smaller C.S.A. ↔ High Résistance )

The Three Test Results can know be put Onto the “ Test Result Sheet “

Domestic Electrical Installation Certificate : “ Test Results “ > Circuit Impedance ( Ω ) :
( Ring Final Circuit(s) Only / Measured End–to–End , > Test Results in Box <

“ Résistance and the Conductor “ 2392-10

Résistance is directly proportional to Length and inversely proportional to “ C.S.A” simply this means that More Length > More Résistance ,
and Less Length > Less Résistance , Also the Greater the C.S.A. the Less the Résistance , and the Smaller the C.S.A. the Greater the Résistance

The Circuit Design why ? : Apprentices

Lighting circuits are almost always wired in Parallel - from strings of Christmas tree lights to the lights in your home - since adding another light to the parallel circuit does not affect the voltage reaching the lights already in the circuit. If for example you were to wire two 12V bulbs in series with a 12V battery, each bulb would receive only 6 Volts. Wired in Parallel each bulb still receives the 12 Volts it needs. Also, if one bulb fails, the rest of the bulbs will remain lit ,

Circuit Résistance in Parallel

Résistance is directly proportional to length and inversely proportional to c.s.a. Simply this means that more length, more Résistance, and less length less Résistance. Also the greater the c.s.a. the less the Résistance, and the smaller the c.s.a. the greater the Résistance.

 

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Amberleaf ( 6 – Pack Tonight )

Passed My 2392-10 Certificate / Fundamental Inspection , Testing & Initial Verification :

Have a lot off 2391-10 stuff , when I get a chance I’ll down load them ,

Jason I’ll need to use a new folder Amberleaf , how will I word it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Testing –

The Obtaining and Recording of the Installations ( Psc ) & ( Ze ) Details :

When Obtaining the Values of either the Psc & Ze at the Origin of the Installation three Methods appear to be Acceptable :

(1) By Enquiry : Usually given upon request to the local Regional Electricity Board , it is common practice for them to quote
A maximum value “ this usually being 16kA for the Prospective Short Circuit Current and earth loop values of 0.35Ω for TN-C-S 0.8Ω for a TN-S system , O.S.G. p-11

(2) By Calculation :
The Designer , using information given , with regard to cable sizing , length of run from the sub-station , etc , can calculate the (PSC ) & the Phase Earth Loop Impedance at the Origin of the Installation ,

(3) By Direct Measurement :
Using a Instrument a direct measurement can be made for the ( PSCC ) ↔ ( PFC ) & ( Ze ) of the Installation
at the Supply intake Terminals ,

* Test results do not specify whether the actual recorded instrument reading is that of a ( Phase / Neutral or a ( Phase / Phase short circuit ,
Although the worst scenario is a short circuit fault across the three phase it appears that a Phase / Neutral measurement is acceptable :

“ Measurement of the Prospective Earth Fault Current “
To measure the Earth Fault Current as a direct reading in Amps , the Instrument ( Neutral Lead can be Connected to the Earth Block )
with the Instrument still set on the current range what will now be measured is the Prospective Earth Fault Current ,

* ( Psc ) range kA ,
By Using this method it saves you having to divide the Earth Loop Impedance reading previously obtained into the supply voltage to
obtain the Earth Fault Current ,
Prospective Short Circuit Current to be measured and recorded , but where the Prospective Earth Fault Current exceeds that of the Short Circuit Current then this Value should be recorded in its place ,
the value of whichever is the Greater should be recorded on the Certificate as the Prospective Fault Current ( Pfc )

“ Measurement of the Short Circuit Current “
“ Range kA “
The test is made using a dedicated ( Psc ) Instrument connected as ( Line & Neutral )
( Most Earth Loop Impedance Instruments incorporate the facility for the measurement of the Phase-Neutral Prospective Short Circuit Current ,

The Protective Devices at the Point of Test must have a Short Circuit Rating in Excess of the reading taken ,
( the Exemptions from this Requirement are when MCBs etc. are used for Overload Protection and BS-1361 or BS-88
Protective devices with suitable operating Characteristics { POSITIONED on the SUPPLY SIDE ϟϟ }

Contractors will Only have Instruments capable of Psc measurement’s at 230V , so a problem will arise on Three Phase systems where a
Ph – Ph –Ph measurement is required , if a 3-Phase measurement is required it has unfortunately become common practice to multiply
The Single Phase recorded measurement by a factor of ( Ѷ 3 )
On Three Phase systems it should be policy to measure and record both the Three Phase Short Circuit Current ( Ph-Ph-Ph ) and
Single Phase Short Circuit Fault Current ,
( Unfortunately Obtaining the ( Ph-Ph-Ph ) Short Circuit Current is easier said than done ,

The Earth Fault Loop Impedance ( Zs ) is made up of the Impedance of the Consumers Phase & Protective Conductors ( R1 and R2 )
Respectively , and the Impedance external to the Installation ( Ze ) Impedance of the Supply ,
As the value of ( Ze ) will be obtained from the Electricity Company for the Initial assessment of the Installation ,
The maximum Impedance allowed for the Phase & Protective Conductors can be determined from :
( Zs + Ze + R1 + R2 )

Radial Circuit :
13Amp Immersion heater circuit protected by a Type B 16amp MCB , wired in 2.5mm2 PVC sheathed cable with a 1.5mm2 CPC
Supplied from 230 volt single phase TN-C-S system , what is the maximum length of run ? ( mV 19.51 x A 16 = 31.2m ) 2391 **

If = Uo / Zs : ( 230v Phase to Earth ) 230 ÷ 0.93Ω = 247A

Zs : R1 , 0.5Ω + R2 , 0.43Ω = 0.93Ω

 

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2392-10 Domestic Electrician’s ←←←←←←←←

-&- are asking for : ( Calculating of R1+R2 ) Calculating of MΩ in parallel , look back through the pages , Ps : Earth Electrode Calculating I got 9 off the this , BE AWARE ↔↔↔↔↔↔↔↔↔↔ Ambeleaf

 

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2392-10

i) Prospective Short Circuit Current is due to a Fault between Phases on Phase and Neutral :
ii) Prospective Earth Fault Current is due to a Fault between Phase and Earth :

i) Prospective Fault Current : intake position – house , ( PFC = 230 ÷ 0.2 = 1150.A / 1.15kA :
ii) Prospective Fault Current : complex “ Dist , Board “ ( PFC = 230 ÷ 0.46 = 500A / 0.5 kA :

Remember to look through your Cals on the pages , its your Butt on the Line , 2392-10 ←←←
You need to think like a Tester ,

 

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Visual Inspection 0nly :

Until an obvious fault develops, most householders appear to assume that their electrical installations are
safe, and will remain so forever. Even those who appreciate that electrical installations eventually need
to be checked appear reluctant to pay for a full BS-7671-style periodic inspection, except perhaps when
they are buying or selling a property. Therefore, even given the significant limitations of ‘visual inspection
only’ such inspection by a competent person can usefully serve to identify damage, deterioration and, to
some extent, defects, which might otherwise go unnoticed by those using the installations.

in principle, visual inspection of the electrical installation in a dwelling by a competent person is an important part of the assessment of the condition of that installation. Visual inspection can identify damage, deterioration and
some defects in installations. Given the potential benefits, the NICEIC does not consider the practice of ‘visual inspection only’ to be non-compliant with the requirements of BS-7671,
provided that:
The visual inspection is carried out by an electrically competent person with good knowledge and experience of the electrical

installation practices existing at the time the installation was first constructed.

* The inspection is carried out in accordance with all the requirements of BS 7671 that are applicable to visual inspection.
* The limitations of ‘visual inspection only’ are made clear in writing to the person ordering the work.
* No claim is made that ‘visual inspection only’ can or will fully determine whether an installation is safe for continued use.
* An objective report of the findings of the visual inspection is given to the person ordering the work, whether or not specifically requested by that person.
* The scope of the condition report includes all the aspects of the model periodic inspection report given in BS 7671 which are relevant to visual inspection.
* Visual condition reports do not include items that can only be checked with test instruments ( such as the adequacy of earthing arrangements ).
* Any quotation for proposed remedial work is given separately from the visual condition report.
*A full periodic inspection is recommended to the customer if it is suspected that the installation is in an unsafe condition.

 

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THE 17TH EDITION & LOCATIONS CONTAINING ….. ( 2392-10 )

A BATH OR SHOWER

INTRODUCTION
Section 701 of BS7671:2008 The 17th Edition is the new section covering locations containing a
bath or shower. The bathroom regulations Section 601 of the 16th Edition were based on the draft
international standard IEC 364. The 17th Edition has been based on both IEC 364 Section 701 and
the new European harmonised document HD 384 Part 7, within Section 701 of the 17th Edition.
HD 384, Section 701 has been published. The 17th Edition absorbs the regulations in these standards.
As with the 16th Edition, regulations in 701 are specific requirements that add to or modify the general
requirements of Parts 3, 4 & 5. The numbers following the section number relate to the chapter and
sections of the general parts e.g. 701.415.2 supplementary equipotential bonding is an extension of
section 415.2 in Chapter 41.
The scope of Section 701 is the same as the 16th Edition, any location where there is a fixed bath or
shower. This includes communal showers and baths in sports facilities and accommodation buildings,
hotels and similar as well as domestic bathrooms. It does not include emergency showers in industrial
areas or laboratories and medical treatment locations. However, there are no special requirements recorded for medical treatment locations. Electrical Contractors’ Association
KEY FACTSHEET
MAIN CHANGES
OMISSIONS FROM 16TH EDITION
601-01 Zone 3 is deleted.
601-04 Supplementary equipotential bonding is not required provided that all circuits at the location are
protected by a 30 mA RCD and there is continuity between the extraneous-conductive-parts and the
protective equipotential bonding.
601-07 Wiring systems is deleted.
There are no restrictions as to where cables may be installed but any surface enclosures, including
trunking, installed in the zones must have minimum rating IPX4.

ADDITIONS
701.411.3.3 Additional protection by 30 mA RCDs is required for all circuits serving equipment in the location.
701.512.3 Low voltage socket-outlets may be installed, but must be at least 3 m from the zone 1
boundary and protected by a 30 mA RCD.
701.753 Particular requirements for electric floor heating systems.

DETAILS OF REQUIREMENTS
ZONES
701.32.1 The upper height limit of all zones is 2.25 m. Above 2.25 m is outside of all zones.
701.411.3.3 ADDITIONAL PROTECTION BY RCDS
All circuits must be protected by RCDs. A single RCD may protect a group of circuits.

THE 17TH EDITION & LOCATIONS CONTAINING
A BATH OR SHOWER
INTRODUCTION
Section 701 of BS7671:2008 The 17th Edition is the new section covering locations containing a
bath or shower. The bathroom regulations Section 601 of the 16th Edition were based on the draft
international standard IEC 364. The 17th Edition has been based on both IEC 364 Section 701 and
the new European harmonised document HD 384 Part 7, within Section 701 of the 17th Edition.
HD 384, Section 701 has been published. The 17th Edition absorbs the regulations in these standards.
As with the 16th Edition, regulations in 701 are specific requirements that add to or modify the general
requirements of Parts 3, 4 & 5. The numbers following the section number relate to the chapter and
sections of the general parts e.g. 701.415.2 supplementary equipotential bonding is an extension of
section 415.2 in Chapter 41.
The scope of Section 701 is the same as the 16th Edition, any location where there is a fixed bath or
shower. This includes communal showers and baths in sports facilities and accommodation buildings,
hotels and similar as well as domestic bathrooms. It does not include emergency showers in industrial
areas or laboratories and medical treatment locations. However, there are no special requirements
recorded for medical treatment locations.

THE 17TH EDITION & LOCATIONS CONTAINING A BATH OR SHOWER
701.413 ELECTRICAL SEPARATION
May be used as a protective measure for a single item of equipment or a single socket outlet.
Not to be used with electric floor heating systems.

701.414 EXTRA LOW VOLTAGE - SELV OR PELV
All live parts to be insulated or contained within enclosures, minimum IPXXB or IP2X.

701.415 ADDITIONAL PROTECTION SUPPLEMENTARY EQUIPOTENTIAL BONDING

Where required, supplementary bonding shall connect protective conductors of each circuit to each other
and to accessible extraneous-conductive-parts. This includes: metal water, gas and waste pipes, metallic
air conditioning and heating systems, accessible structural parts of the building.
Metal door and window frames and similar are not normally extraneous-conductive-parts unless connected
to structural steel.
The bonding does not necessarily have to be in the location. It may be an adjacent room (linen cupboard)
or above a ceiling. It must be accessible for inspection, testing and maintenance.

SUPPLEMENTARY BONDING IS NOT REQUIRED AND MAY BE OMITTED:
(i) where main bonding is provided in accordance with 411.3.1.2, and
(ii) all final circuits meet the required disconnection times 0.4 sec for TN systems, 0.2 sec for TT
systems, and
(iii) all circuits have additional protection by 30 mA RCD, and
(iv) all extraneous-conductive-parts (metal water pipes) in the location are electrically continuous
and effectively connected to the protective equipotential bonding.
Where the main pipework of water distribution and central heating systems are pvc, short sections of
copper pipes connecting taps, radiators and the like are not considered to be extraneous-conductive parts
because they are unlikely to introduce Earth to the location. Supplementary bonding is therefore
not required.
Supplementary equipotential bonding is unlikely to be required on a new installation. It may be required
where alterations and additions are being made to an installation (it may already in place). In this
situation, circuits that are not being affected by the alterations do not require upgrading to meet the
requirements of 701.411.3.3 protection by 30 mA RCD.

701.5 SELECTION AND ERECTION OF EQUIPMENT, SWITCHGEAR AND CONTROLGEAR

701.512.2 EXTERNAL INFLUENCES
The following does not apply to the switches and controls of fixed current using equipment and the cords
of pull cord switches.
All equipment must be suitable for the zone in which it installed.
Requirement for equipment:
(i) Zone 0 - IPX7
(ii) Zones 1 & 2 IPX 4 (except in Zone 2, shaver sockets to BS EN 61558-2-5 located where
direct spray from showers is unlikely).
(iii) IPX5 anywhere where equipment may be exposed to water jets.
THE 17TH EDITION & LOCATIONS CONTAINING A BATH OR SHOWER
701.512.3 ERECTION OF SWITCHGEAR, CONTROLGEAR AND ACCESSORIES
(i) Zone 0 - no switchgear or accessories are permitted
(ii) Zone 1 - only switches for SELV circuits and equipment - max 12V a.c. rms or 30V ripple free
d.c. may be used. Safety source to be outside zones 0, 1 & 2.
(iii) Zone 2 as (ii) above except, shaver sockets to BS EN 61558-2-5 may be fitted.
(iv) 13 amp socket-outlets may be installed, must be at least 3 m from the zone 1 boundary.
13 Amp socket outlets may be
installed 3m horizontally from the
boundary of Zone 1 and must be
protected by a 30mA RCD
*Zone 1 if the space is accessible without the use of a tool.
Spaces under the bath accessible only with the use of a tool
are outside the zones.
OR SHOWER
701.55 CURRENT-USING EQUIPMENT
In zone 0 current-using equipment must
(i) comply with the relevant product standard
(ii) be suitable for use in Zone 0
(iii) installed to manufacturer’s instructions
(iv) be fixed and permanently connected
(v) SELV not exceeding 12 V a.c. rms or 30 V ripple-free d.c. Safety source to be outside Zone 0,1 & 2
In zone 1 current-using equipment must
(i) be fixed and permanently connected
(ii) be suitable for use in Zone 1
(iii) installed according to manufacturer’s instructions
Equipment that may be installed
(i) Whirlpool units
(ii) Electric showers
(iii) Shower pumps
(iv) Equipment protected by SELV or PELV nominal voltage not exceeding 25 V a.c. rms or 60 V
ripple-free d.c.
Safety source to be outside Zone 0,1 & 2
(v) Ventilation equipment
(vi) Towel rails

(vii) Water heaters
(viii) Luminaires
In zone 2 current-using equipment must be
(i) permanently connected, the means of connection must be outside of zone 2
(ii) suitable for use in a location containing a bath or shower
(iii) installed according to manufacturer’s instructions

701.753 ELECTRIC FLOOR HEATING SYSTEMS
Heating cables and thin sheet heating elements must:
(i) comply with relevant product standards
(ii) have a metal sheath, or
(iii) have a metal enclosure, or
(iv) be covered with a fine metal mesh.
Unless the protective measure SELV is applied, metal sheaths, enclosures and grids must be
connected to the circuit cpcs
The protective measure ‘electrical separation’ is not permitted

RCD Ratings :

The rating of an RCD has nothing to do with its ability to handle the current to the appliance or the circuit protected, but is the value of residual current at which it will operate. Thus, an RCD in a typical domestic situation may well be able to switch off the load current of 40A but be rated at a residual current of 30mA ( thirty thousandths of an ampere ). RCDs are made with a wide range of ratings, but by far the most common are 30mA and 100mA

 

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BS 1362 specifies breaking-time/current characteristics only for fuses with a current rating of 3 A (marked in red ) or 13 A (marked in brown ). Examples for the required breaking-time ranges are

• For 3 A fuses: 0.02–80 s at 9 A, < 0.1 s at 20 A and < 0.03 s at 30 A.
• For 13 A fuses: 1–400 s at 30 A, 0.1–20 s at 50 A and 0.01–0.2 s at 100 A.

3 A fuses are intended mainly for small load (< 750 W) appliances, such as radios and lights. 13 A fuses are for larger load (<3.2 kW) appliances such as heating and heavy-duty electric motors , .

BS 1362 requires that plug fuses with any other current rating are marked in black. 5 A fuses are also commonly used, for medium load (1250 W max.)

Syntax Error :
Appears when the figures are entered in the wrong order ,
x2 ↔ Multiplies a number by itself , i.e. 6 x 6 = 36 , on the calculator this would be 6 x2 = 36 , when a number is
multiplied by itself it is said to be Squared ,

x3 ↔ multiplied a number by itself and then the total by itself again i.e. when we enter 4 on calculator x3 = 64 .
when a number is multiplied in this way it is said to be Cubed :

√ ↔ Gives the number which achieves your total by bring multiplied by itself i.e. √ 36 = 6 This is said to be the Square root
of a number and is the opposite of Squared :

3√ ↔ Gives the number which when multiplied by itself three times will be the total , 3√ 64 = 4 this is said to be the Cube root ,

Brackets :
these should be used to carry out a calculation , within a calculation .
Example calculation :
………. 32
( 0.8 x 0.65 x 0.94 )
Enter into calculation 32 ÷ ( 0.8 x 0.65 x 0.94 ) = ?

 

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Utilising the Fault Current 17th Edition : ( Table 41.2 ) Revision :

Sticking with our light circuit scenario and assuming that the light circuit is protected by a 5 amp re-wireable type fuse then the maximum allowable earth fault loop impedance given by BS-7671 wiring regulations is 9.58Ω. This value is for the total resistance in the fault loop described above.

Ohms Law : it is fundamental to electrical design and I will show you why. Ohms Law states that when current flows through a load or Résistance then the voltage that you can measure across the load will be equal to the product of the Résistance and current.

Simply, VOLTAGE = RESISTANCE X CURRENT which is normally shortened to V=IR or I=V/R or R=V/I (/ means divided by for non-mathematic persons )

We can now use Ohms Law to calculate the fault current for our maximum earth fault loop impedance of 9.58Ω that we extracted from the wiring regulations knowing that the supply voltage to our house is 230V.

Using I=V/R we have I = 230V ÷ 9.58Ω and a few taps of the calculator gives the current as 24 amps.

Thus, 24 amps of current is going to flow through a 5 amp fuse. The fuse wire gets hot, melts and breaks the circuit. So we have an Automatic Disconnection of Supply or ADS.

Basic Protection :

Protection against electric shock under fault free conditions. (I.E. provision of insulation on wires and plastic covers on equipment)
Used to be referred to as Direct Contact which was the contact of persons or livestock with live parts which may result in electric shock. Basically, if live parts are such as conductors and terminals are protected by insulation (basic protection) then a person cannot come into direct contact with lethal voltages.

Residual Current Device: 2392-10

When you turn an appliance on such as a cooker, it places a load on the electrical circuit and current flows through the load which provides the heat. Current flows down the live or LINE conductor and returns along the NEUTRAL conductor back to the origin of the supply.

The current that returns up the neutral from the load should equal the current that flows down the line to the load.

If there is a difference in theses currents then current is being 'lost' somewhere and this will be a leakage to earth. If this leakage to earth is via you then you may be receiving an electric shock.

The RCD cleverly monitors the current flowing out and the current flowing back and if they differ by an amount determined by the rating of the RCD then it automatically disconnects the supply.

RCDs used to protect sockets and wiring in an domestic installation are rated at 30mA (milli amps).

Apprentice :
Continuity in the protective earth conductor.

There are no breaks so for instance, the earth connection on the last light point in the circuit is continuous right back the main earth terminal back at the consumer unit.

Continuity in ring circuits.

To avoid cable being overloaded it is important that the ring is unbroken.

Insulation Resistance.

Checks to ensure that there are no breakdowns in insulation between live conductor and live conductors and the earth conductor. This test will pick up cable damaged during installation. The circuits are tested at a DC voltage of 500V. ( or 250v d.c SELV / PELV - check table 61 regs ,

Polarity

That there Line, Neutral and Earth conductors are all correctly connected at sockets and light outlets. (check that single pole switches are installed in the Line and not the Neutral)

Earth Loop Fault Impedance

This tests the resistance to a fault current due to a short occurring between Line and Earth. If the resistance is too high a dangerous shock voltage would exist.

Prospective Fault Current

This is the value of current that can flow in your wiring in a fault condition. Values can range from 1000 amps to 16000 amps. circuit breakers and fuses have sufficient rating to interrupt the current.
Operating time for Residual Current Devices (RCDs RCBOs).
We test a 50% of the current rating to check that they do not trip.
We test at 100% and 500% of current rating and record the operating time is within specified limits. If the device does not operate within limits then you could get a shock when you chop your cable with your lawn mower!

Earth Electrode Resistance

This only applies if you do not have an earth connection supplied by the electricity supplier and the earth is provided by a rod driven into the ground. Usually found in more rural locations and known as a TT supply.

How Building Regulations now affect Domestic Electrical Installations : 2392-10

Stay legal with the Building Regulations :

Building Regulations are statutory and you can be prosecuted for failing to comply with them. Failure to comply is in fact a criminal offence.

Building Regulations 2000 Statutory Instrument No. 2531 are made under powers provided in the Building Act 1984 and applies in England & Wales.

The purpose of the Building Regulations is to provide for the Health & Safety of people in and around buildings and also provide for matters such as energy conservation, access and use.

Regulation 4 of the Building Regulations 2000 as amended requires that

4.(1) Building work will be carried out so that:
(a) it complies with the applicable requirements contained in Schedule 1 (Parts A to P); and
(b) in complying with any such requirement there is no failure to comply with any other requirement.
(2) Building work shall be carried out so that after it has been completed:
(a) any building which is extended or to which material alteration is made; or

(b) any building in, or in connection with, which a controlled service or fitting is provided, extended or materially altered; or

(c) any controlled service or fitting complies with applicable requirements of Schedule 1 (Parts A to P) or, where it did not comply with any such requirement, is no more unsatisfactory in relation to that requirement than before the work was carried out.
Amendment No. 2 to the Building Regulations introduced Part P complete with a definition of Electrical Installation

Part P Electrical Safety (Schedule 1 to Building Regulations) - Requirement
Design and installation

P1. Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.
Limits of application
The requirements of this part apply only to electrical installations that are intended to operate at Low – Voltage or Extra Low Voltage and are:

(a) in or attached to a dwelling

(b) in the common parts of a building serving one or more dwellings, but excluding power supplied to lifts

(c) in a building that receives its electricity from a source located within or shared with a dwelling; and

(d) in a garden or in or on land associated with a building where the electricity is from a source located within or shared with a dwelling.

So what do these regulations mean where domestic electrical work is concerned ?
Firstly, that electrical work in dwellings is now a controlled service under building regulations because Part P of Schedule 1 sets out the requirement P1 as detailed above which means that failure to satisfy the requirements is an offence.

Secondly, for electrical work you use the guidance offered in Approved Document P , Electrical Safety – Dwellings , for the purpose of complying with P1. Furthermore, the guidance advises that the requirement of P1 will be met by adherence to the 'Fundamental Principles' for achieving safety given in BS-7671 chapter 13 so effectively giving a statutory status to BS -7671.
Thirdly, you must also take into account other parts of schedule 1 which will be invoked by activities carried during electrical installation work.

These are:
Part A - Structure
Depth of chases in walls and sizes of holes and notches in joists

Part B - Fire Safety
Provision of fire alarm and fire detection systems, fire resistance of penetrations through floors and walls

Part C - Site Preparation
Resistance to moisture of cable penetrations through walls

Part E - Resistance to Passage of Sound
Installations must not degrade the resistance of passage to sound in the building

Part F - Ventilation
When adding extractor fans

Part L1 - Conservation of Fuel and Power
Lighting systems to be supplied with appropriate lamps and controls so that energy can be used efficiently

Part M - Access and facilities for the disabled
Heights of switches and socket outlets.

For example - you live in a flat with another flat above you. You decide to have some downlighters fitted into the ceiling of your lounge.

Account must be taken of Part B - Fire Safety regarding fire resistance as the ceiling will be penetrated to fit the downlighters thus weakening the fire barrier and resistance to the spread of fire.

Also Part E - Resistance to Passage of Sound must be observed as the ceiling provides an acoustic barrier.
To deal with this particular installation problem there are available on the market fire rated mains and low voltage downlighters which comply with both Part B and E requirements.

 

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2392-10
*Applicable with effect from the 1st July 2008 when new 17th edition of BS-7671 ,

Defects in the existing installation that effect the safety of the alteration or addition must be made good.

Most likely Defects to be found which will affect New Work

No : Main Protective Bonding Conductor :
No : Supplementary Protective Bonding Conductors ( where Required ) in bathroom but now requires RCD protection*
No : RCD Protection on sockets*
No : RCD Protection for buried cables in walls*

Alternating Current (AC)

The mains supply current waveform is a sine wave which has the form , ↔ One Cycle ↔ It repeats 50 cycles every second which using the international symbol for frequency is written as 50 Hz
Amplitude / Time !!!!

Fault finding & Breakdowns :
Electrical fault finding by it's very nature is a process of elimination.

Firstly the customer reporting the fault will be asked some seemingly simple questions such as what happened ?, when did it happen? What usually happens? What isn't happening now etc.

Then an inspection will take place looking for signs of wear and tear, mechanical damage to cables or accessories, signs of overheating, corrosion, burning and even listening for strange noises from equipment etc.

If the problem is not evident after the initial visual check then some electrical testing will have to take place in order to find the fault in the hidden cables. This can be a time consuming process and will mean isolation of the supply for a time.
Once the fault is identified it can then be rectified. This may mean a new component or accessory or even replacement of the faulty cable.

RCDs : Apprentices’ ,

One of the major changes in the 17th Edition of the IEE Wiring Regulations is the requirement of RCD's to protect circuits where the cables are buried in walls at a depth of less than 50mm and not mechanically protected. In a domestic property this is likely to include most if not all the circuits.

So what exactly is an RCD ?

An RCD is an electrical safety device specially designed to immediately switch the electricity off when electricity "leaking" to earth is detected at a level harmful to a person using electrical equipment. An RCD offers a high level of personal protection from electric shock. Fuses or overcurrent circuit breakers do not offer the same level of personal protection against faults involving current flow to earth. Circuit breakers and fuses provide equipment and installation protection and operate only in response to an electrical overload or short circuit. Short circuit current flow to earth via an installation's earthing system causes the circuit breaker to trip, or fuse to blow, disconnecting the electricity from the faulty circuit. However, if the electrical resistance in the earth fault current path is too high to allow a circuit breaker to trip (or fuse to blow), electricity can continue to flow to earth for an extended time. RCDs (with or without an overcurrent device) detect a very much lower level of electricity flowing to earth and immediately switch the electricity off.

RCDs have another important advantage - they reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. This is particularly significant in older installations.

How they Work :

RCDs work on the principle "What goes in must come out". They operate by continuously comparing the current flow in both the Active (supply) and Neutral (return) conductors of an electrical circuit.
If the current flow becomes sufficiently unbalanced, some of the current in the Active conductor is not returning through the Neutral conductor and is leaking to earth.

RCDs are designed to operate within 10 to 50 milliseconds and to disconnect the electricity supply when they sense harmful leakage, typically 30 milliamps.

The sensitivity and speed of disconnection are such that any earth leakage will be detected and automatically switched off before it can cause injury or damage. Analyses of electrical accidents show the greatest risk of electric shock results from contact between live parts and earth.

Contact with earth occurs through normal body contact with the ground or earthed metal parts. An RCD will significantly reduce the risk of electric shock, however, an RCD will not protect against all instances of electric shock. If a person comes into contact with both the Active and Neutral conductors while handling faulty plugs or appliances causing electric current to flow through the person's body, this contact will not be detected by the RCD unless there is also a current flow to earth.

On a circuit protected by an RCD, if a fault causes electricity to flow from the Active conductor to earth through a person's body, the RCD will automatically disconnect the electricity supply, avoiding the risk of a potentially fatal shock.

Examples of equipment recommended to be protected by a RCD:

• Hand held electric power tools, such as drills, saws and similar equipment.
• Tools such as jack-hammers, electric lawn mowers.
• Equipment on construction sites.
• Equipment such as appliances which move while in operation, such as vacuum cleaners and floor polishers.
• Appliances in wet areas such as kitchens, including kettles, jugs, frying pans, portable urns, food mixers/blenders.
• Hand held appliances such as hair dryers, curling wands, electric knives etc.
• Cord extension leads.

PAT (Portable Appliance Testing)
Inspecting & Testing will be carried out in accordance with the requirements of the following regulations and publications:

Electricity at Work Regulations 1989 :
Health and Safety at Work etc. Act 1974 :
The Code of Practice for In-service Inspection and Testing of Electrical Equipment
The Provision and Use of Work Equipment Regulations 1998 :

Basic fault finding :

Lighting circuits which won't reset.
A common fault is a short circuit on the bulb holder which can get damaged by heat which also makes the cable brittle and then the insulation fails.

unscrew the plastic ceiling rose to check for any signs of corrosion on the wires possibly as a result of some dampness

.2392-10

Possible rewireable fusebox upgrades may also bring to the home owners attention, common hazards such as that of a lighting circuit which DOES NOT have a earth. Where metallic switches ( brass silver etc..) or metallic light fittings are present, there is a risk of electric shock under earth fault conditions.

***URGENT ATTENTION*** is therefore a recommendation.

Also the requirement of 10mm main equipotential earth bonds to gas mains / water mains

2392-10 : Wording for Clients Amber ,

Before
consumer units/fuseboards do not meet current British Standards. This can be due to visible damage e.g., broken fuse carriers, no residual circuit device (RCD) protection, no capacity for additional circuits (requires more circuit ways), or the consumer unit has a wooden back which can be a fire hazard or cable joints which are not terminated properly and are live and exposed. This can be a major factor in causing an electrical fire.

After
consumer units which DO meet British Standards. These consumer units are protected by an RCD (Residual Current Device) which will give you better protection to accommodate the upgrade along with the necessary MCBs (mini circuit breakers) to suit. This gives overload and short circuit protection for the final circuits, as well as the capability of disconnecting a faulty circuit at a faster tripping time

PSCC is Measured as 0.09 Ohm then at a voltage of 230V a fault current of 2555.5A will flow. ( 230 ÷ 0.09 = 2555.6A )

 

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All Main Protective Bonding Conductors are Tested for Continuity.

This is of course done with the System off-Line. You NEVER, EVER, Disconnect Main Protective Bonding Conductors on a Live Installation !

The Résistance of these Conductors should as Low as Possible.

Different classifications of MCB will give different results.

Type 1 requires between 2.7 and 4 times overload current to trip inrequired time. Type 2 requires 4-7 times and type B 3 - 5 times. In all cases you should assume that your MCB is on the upper limit.

* Overload Current can be caused when a) → Excessive mechanical load is applied to an electrical motor← b) a forward/reverse controller attempts to switch a motor to both directions simultaneously c) contamination of a motor terminal bock results in tracking d) an electrician drill through a busbar chamber and touches a live busbar with the drill.

* Current Co-ordination between Conductors and Overcurrent Protection Device is Achieved when a) → In is not less than Ib ← b) In is greater than Iz c) the current causing effect operation (Iz) exceeds 1.45 I2 d) Ib > Iz

* Fireman's Emergency Switches are Provided for the Switching off of a) factory low voltage burglar alarm systems b) interior low voltage discharge lighting systems c) → exterior lighting systems exceeding low voltage ← d) factory fire alarm circuits operating at low voltage.

1 a , 2 a , 3 c Regulation 537.6.3

11 Final ring-circuit wiring can be described as the wiring between a) The cutout-fuse and the electric meter b) the main switch and distribution board c) the distribution board and current using equipment d) the supply cut-out fuse and the remotest point of utilization. 12 A ring final sub-circuit is run in pvc conduit. How many single core cables are required? a) 3 b) 4 c) 5 d) 6 14 An earth conductor is connected to the supply sheath of a lead armoured cable at a hospital intake. Is this system a) TT b) TN-C c) TN-S d) TN-C-S 15 An electric fire having an element exposed to touch would allow the risk of an electric shock by a) prospective contact b) earthing contact c) indirect contact d) direct contact. 18 An extra-low-voltage system is electrically separated from earth is called a) F.E.L.V. b) **** S.E.L.V. c) non-conducting d) earth free.

11 c : 12 , 6 (2 x brown ) (2 x cpc ) (2 x blue ) : 14 c TN-S see page 33 : BS 7671:2008 : 15 d direct contact 18 definitions , p-29

4 A d.c. voltage of 120V between conductors is classified as being a) extra-low voltage b) Low-voltage c) Reduced-low-voltage d) S.E.L.V.
6 Which of the following describes a TN-C-S system a) earthing is independent of the supply cable b) the consumers earth terminal is connected to the incoming cable sheath c) protective and neutral conductors are combined d) supply system has no earth
8 Which of the following is NOT a classification of external influences? a) Current rating b) Environmental conditions c) Construction of a building d) Utilization.
10 An electrical installation should be arranged in such a way as to avoid hazards in the event of a fault and to allow safe operation, maintenance and testing when required. One method of complying with this is to a) Connect all circuits as radial circuits b) Connect all circuits as ring final sub-circuits c) Divide the installation into separate circuits d) divide the installation into categories of circuits

4 b see Part 2 definitions 'low voltage' : 6 c TN-C-S : p – 33 : 8 a refer to appendix 5 BS 7671:2008 p – 318 : 10 c see Regulation 314.1.

The principle of SELV is that by reducing the voltage to 50V or below the risk of electric shock is reduced and additionally with SELV the equipment supplied through a BS-EN 61558-1 transformer will have no return path to the source given that there is no connection to earth. Regulations within BS 7671 regarding the use of SELV as a protective measure can be found in Chapter 41 specifically regulation 414.1 / 414.4.5

Insulation Resistance :

* Before testing check:
* Pilot or indicator lamps should be disconnected
* Voltage sensitive equipment should be removed, such as dimmer switches, timers, controllers, starters and RCDs*
* Lamps should be removed
* There is no electrical connection between any phase, neutral or protective conductor
Insulation Resistance Method
* Set the instrument to the Megohms scale

* MΩ (Millions of ohms)
* Test voltage 500v

* Readings should be 1.0MΩ but should be investigated below 2 MΩ

Insulation Resistance
* Test between the phase and neutral conductors connected together and earth at the consumer unit

* For circuits containing 2 way or 2 way and intermediate, switched must be operated one at a time and the circuits subjected to an additional test

Insulation Resistance
* Conducted to detect short circuits and high resistances in circuits

* Considered a ‘pressure test’, putting approximately twice the nominal voltage through a completed circuit

Zero or Null leads

* When measuring the resistance of a length of cable, we must take into account the resistance of the leads
* Null the leads
* If it is an older instrument, we need to take the reading of the leads and subtract it from the total reading of the measured length of cable

 

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Dimmer Buzzing :

If you hook up a really cheap dimmer switch, you may notice a strange buzzing noise. This comes from vibrations in the bulb filament caused by the chopped-up current coming from the triac.
you know that electricity flowing through a coiled length of wire generates a substantial magnetic field, and fluctuating current generates a fluctuating magnetic field. If you've read How light Bulbs work , you know that the filament at the heart of a light bulb is just a coiled length of wire. It makes sense, then, that this coiled filament becomes magnetic whenever you pass current through it, and the magnetic field fluctuates with the AC current.

Normal undulating AC current fluctuates gradually, so the magnetic field does, too. The chopped-up current from a dimmer switch, on the other hand, jumps in voltage suddenly whenever the triac becomes conductive. This sudden shift in voltage changes the magnetic field abruptly, which can cause the filament to vibrate -- it's rapidly drawn to and repelled by the metal arms holding it in place. In addition to producing a soft buzzing sound, the abruptly shifting magnetic field will generate weak radio signals that can cause interference on nearby TVs or radios !

Better dimmer switches have extra components to squelch the buzzing effect. Typically, the dimmer circuit includes an inductor choke, a length of wire wrapped around an iron core, and an additional interference capacitor. Both devices can temporarily store electrical charge and release it later. This "extra current" works to smooth out the sharp voltage jumps caused by the triac-switching to reduce buzzing and radio interference.

Some high-end dimmer switches, such as the ones commonly used in stage lighting, are built around an autotransformer instead of a triac. The autotransformer dims the lights by stepping down the voltage flowing to the light circuit. A movable tap on the autotransformer adjusts the step-down action to dim the lights to different levels. Since it doesn't chop up the AC current, this method doesn't cause the same buzzing as a triac switch.

There are a lot of other dimmer switch varieties out there, including touchpad dimmers and photoelectric dimmers, which monitor the total light level in a room and adjust the dimmer accordingly. Most of these are built around the same simple idea -- chopping up AC current to reduce the total energy powering a light bulb. At the most basic level, that's all there is to it.

Some high-end dimmer switches, such as the ones commonly used in stage lighting, are built around an autotransformer instead of a triac. The autotransformer dims the lights by stepping down the voltage flowing to the light circuit. A movable tap on the autotransformer adjusts the step-down action to dim the lights to different levels. Since it doesn't chop up the AC current, this method doesn't cause the same buzzing as a triac switch.

There are a lot of other dimmer switch varieties out there, including touchpad dimmers and photoelectric dimmers, which monitor the total light level in a room and adjust the dimmer accordingly. Most of these are built around the same simple idea -- chopping up AC current to reduce the total energy powering a light bulb. At the most basic level, that's all there is to it.


* An inductor is about as simple as an electronic component can get -- it is simply a coil of wire. It turns out, however, that a coil of wire can do some very interesting things because of the magnetic properties of a coil :
In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. If you have read , then you know that a battery has two terminals. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.

Incandescent lamp physics

A typical incandescent lamp take power and uses it to heat up a filament until it will start to radiate light. In the process about 10% of the energy is converted to visible light. When the lamp is first turned on, the resistance of the cold filament can be 29 times lower than it's warm resistance. This characteristic is good in terms of quick warmup times, but it means that even 20 times the steady-state current will be drawn for the first few milliseconds of operation. Lamp manufacturers quote a typical figure for cold lamp resistance of 1/17 th of the operational resistance, although inrush currents are generally only ten times the operational current when such things as cable and supply impedance are taken into account. The semiconductors, wiring, and fusing of the dimmer must be designed with this inrush current in mind. The inrush current characteristic of incandescent (tungsten filament) lamps is somewhat similar to the surge characteristic of the typical thyristors made for power controlling, making them a quite good match. The typical ten times steady state ratings which apply to both from a cold start allow many triacs to switch lamps with current ratings close to their own steady state ratings.

Because lamp filament has a finite mass, it take some time (depending on lamp size) to reach the operating temperature and give full light output. This delay is perceived as a "lag", and limtis how quicly effect lighting can be dimmed up. In theatrical application those problems are reduced using preheat (small current flows through lamp to keep it warm when it is dimmed out).

The ideal lamp would produce 50% light output at 50% power input. Unfortunately, incandescents aren't even close that. Most require at least 15% power to come on at all, and afterwards increase in intensity at an exponential rate.

To make thing even more complicated, the human eye perceives light intensity as a sort of inverse-log curve. The relation of the the phase control value (triac turn on delay after zero cross) and the power applied to the light bulb is very non-linear. To get around those problems, most theatrical light dimmer manufacturers incorporate proprietary intensity curves in their control circuits to attempt to make selected intensity more closely approximate perceived intensity.

“ Resistance Ohmmeters “

Once a month, take a measurement of each Resistor. Over a period of time, show how the instrument is performing , ( Set of low-value resisters )

i.) Low-resistance ohmmeters A set of suitable resistors could be used to assess the instrument; suitable values could be 0.5 Ohms , 0.1 Ohms and 10 Ohms

i.) High-Résistance ( Insulation Résistance ) Ohmmeters A set of suitable Resistors could be used to assess the Instrument; suitable values could be 0.5MΩ 1.0MΩ and 10MΩ.

The Resistor values chosen merely reflect common bands of Résistance that are generally encountered when Testing Electrical Installations. Other values of Résistance, indeed, greater numbers of Resistors, could be used to assess Résistance Ohmmeters across the spectrum of Résistance.

“ Each Resistor on a Connector block ( Test your Instrument ) “

 

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Wiring Regulations in brief :

The Building Regulations , Part P ( which is based on the Fundamental Principles set out in Chapter 13 , BS-7671:2008 ,
In addition , all fixed electrical installations ( i.e. wiring and appliance fixed to the Building fabric such as Socket-Outlets ,
Switches , Consumer Units , and Ceiling fittings ) must now be designed , installed , Inspection , Tested and Certified to BS-7671

Part P of the Building Regulations also introduces the requirement for the cable core colours of all a.c. power circuits to align with BS-7671

Note : Part P only applies to fixed electrical installations that are intended to Operate at Low-Voltage or Extra-Low-Voltage which are not controlled by the Electricity Supply Regulations 1988 as Amended , or the Electricity at Work Regulations 1989 as Amended ,

Why dead tests ?

* Dead tests are performed on an installation prior to energisation
* A dead test will, if carried out correctly, identify faults with a circuit or installation that may be dangerous when energised ,




High value of prospective short circuit current can vary dramatically due to small changes in impedance.

Example: V = Z x I
Therefore: I = 230/0.03 = 7666 Amps
OR: I = 230/0.01 = 23 000 Amps
Notice the vast change in current for a very minor difference in impedance. Obtaining accuracy at very
low impedances is very difficult and a high current is required.

Electrical measuring instruments : ?

( V ) ↔ ( Iv )
R → Ir
( A ) → I

Voltmeter current Iv = V ÷ Rv = 60 ÷ 500 = 0.12A
Resistor current Ir = I – Iv = 5 sub 0.12 amperes = 4.88A
True Value = V ÷ Ir = 60 ÷ 4.88 ohms = 12.3Ω

An alternative method for the second part of this exercise is to consider that the apparent resistor value , 12Ω
Consists of the voltmeter Résistance , 500Ω , in parallel with the unknown resistor R ,

1 ÷ 12 = 1 ÷ 500 + 1/ R
1 / R = 1 ÷ 12 = 1 ÷ 500 = 500 – 12 ( 500 x 12 ,

Therefore : R = 500 x 12 ohms = 6000 ohms
…………………500 – 12 ………. 488 ……...... 12.3Ω

In practice, the most common instances of faulty earthing are:

* Earth connections broken accidentally or corroded through age.
* Earth connections incorrectly made.
* Earth connections not made at all.
* Earth connections removed for some specific purpose and not reinstated.

Double Insulated Equipment: Definitions , p-21

Class II electrical equipment has all exposed metalwork separated from the conductors by two layers of insulation, so that the metalwork cannot become live. There is no earth connection and the operator's safety depends upon the integrity of the two layers of insulation.

PAT , Testing ,
Visual Checks on Hand-Held Portable Equipment Before Use :

Cable :
Signs of mechanical damage, overheating or corrosion
Hardening of outer insulation
Kinking of cable
Coiling of long lengths of cable
A situation where future mechanical damage or corrosion is likely

Plug :
Wires connected to correct terminals and of the correct length
Un-insulated ends of wires completely covered by the screws
Securing screws suitably tight
Fuse of correct rating fitted

Equipment :
Metal casing damaged
Grommet, or other protection at place where cable passes through the casing, damaged or missing
Plastic casing of double insulated equipment damaged
Damaged or defective switches

Note:
An RCD only protects against a Phase to Earth, or a Neutral to Earth fault. It does not protect against a Phase to Neutral fault.

Load Factor

The ratio of the energy actually consumed by a lighting installation over a specified period of time to the energy that would have been consumed had the lighting installation always been operating during the period of time.

Certification

BS 7671 (The Wiring Reguations) states that on completion, all electrical work must be inspected and tested to verify the installation prior to it being energized. A record of this process must be produced in the form of a certificate.

2392-10 rewires ,


Chasing

Electric cables are generally run under floorboards, in the loft and in walls to the electrical accessories. This means that any cables that need to run up or down a solid wall need to be ‘chased in’. Chasing in involves cutting a channel around 25mm wide and 25mm deep into the wall using a special power tool.
Cavity Walls

Some internal walls are not solid but are plasterboard cavity walls. These walls cannot be chased in the conventional way so an alternative method is used. This involves creating holes in the wall at intervals to enable the running of the cables down or up to an accessory.
Floorboards

In order to install cables under floors, carpets will need to be rolled back and the floorboards will have to be lifted. Sometimes the full length of a floorboard cannot be lifted and so it will be cut so that a smaller piece can be removed. Obviously, this would not be done without consulting the homeowner first. Once the cables are in position the board would then be replaced and refixed.
Moving Furniture

Obviously in an inhabited house. There is lots of furniture which could get in the way of access to walls, floorboards etc. It is the homeowners responsibility to move any furniture, beds and the like away from the areas where they are intending to have an electrical accessory. If this is not possible then it can be moved by the electrician. This is an extra to the rewire quote and is charged at an hourly rate. No liability is accepted for any damages to the furniture incurred during this process.

Dust and debris

The processes of chasing walls, making holes and lifting floorboards creates dust and mess and the homeowner must be aware of this. This is kept to a minimum when chasing using a dust extraction system and the liberal use of dust sheets to protect floor coverings. Any dust and debris will be hovered up and removed by the electrician after each days work.

Making Good

Once the whole house has been rewired any chases will need to be filled with plaster and any wholes filled. The homeowner will need the services of a plasterer to do this or alternatively the electrician can do it. This is charged at an hourly rate and would not be to a professional plasterers standard.
Second Fix

The final job to be done, once the plaster has dried, is connect all the electrical accessories and install the customers consumer unit (Fuse board). Then transfer the supply from the old installation to the new. At this point any old accessories and wiring would be removed and the chases left by them filled once again with plaster.

RCDs
have another important advantage - they reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. This is particularly significant in older installations.

( diversity on domestic cookers is to take the load as 10A plus 30% of the remainder of the actual maximum load, then add a further 5A if there is a socket on the cooker unit )

Q: Do I need to carry out an external fault loop impedance (ze) test? Can I just use the declared values from the distributor ? :

A: A direct reading of Ze is always required. This test establishes that the intended means of earthing is actually present. The distributors’ declared values only give an indication of the maximum Ze that would normally be expected on their networks. It doesn’t guarantee that there is not a problem. For instance the earthing

 

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Fundamental Requirements for safety :

The following is a list of basic requirements

1) use good workmanship ,
2) Use approved materials and equipment ,
3) Ensure that the correct type , size and current- carrying capacity of cables are chosen ,
4) Ensure that equipment is suitable for maximum power demanded of it ,
5) Make sure that conductors are insulated , and sheathed or protected if necessary , or are placed in a position to prevent danger ,
6) Joints and connections should be properly constructed to be mechanically and electrically sound ,
7) Always provide overcurrrent protection for every circuit in an installation ( the protection for the whole installation is usually
Provided by the distribution Network Operator , ( DNO ) and ensure that protective devices are suitably chosen for there location and duty they have to perform ,
8) Where there is a chance of metalwork becoming live owing to a fault , it should be earthed , and the circuit concerned should
Be protected by an overcurrent device or a residual current device ( RCD )
9) Ensure that all necessary bonding of services is carried out ,
10) Do not place a fuse , a switch or a circuit breaker , unless it is linked switch or circuit breaker , in an earthed neutral conductor ,
The linked type must be arranged to break all the line conductors ,
11) All single-pole switches must be wired in the line conductor only ,
12) A readily accessible and effective means of isolation must be provided so that all voltage may be cut off from an installation or any of its circuits ,
13) All motors must have a readily accessible means of disconnection ,
14) Ensure that any item of equipment which may normally need operating or attending by persons is accessible and easily operated ,
15) Any equipment required to be installed in a situation exposed to weather or corrosion , or in explosive or volatile environments , should be of the correct type for such adverse conditions ,
16) Before adding to or altering an installation , ensure that such work will not impair any part of the existing installation and that
The existing is in safe condition to accommodate the addition ,
17) After completion of an installation or an alteration to an installation , the work must be inspected and tested to ensure ,
As far as reasonably practicable , that the fundamental requirements for safety have be met ,

Re-vision : Apprentices

* A visual test will also be needed if the test has been carried out to the front of the sockets, and not behind
them, i.e., removing the faceplate screws and testing from behind.

There are 2 methods that can be adopted when conducting a polarity test. These are described below.

Method 1 :
This method is exactly the same as test method one for ‘Continuity Of Protective Conductors’ if we take
a lighting circuit , figure 1, by putting a temporary link between phase and cpc, at the consumers unit and our instrument at lamp holders themselves, we are creating a circuit. When we operate the light switch, the instrument
changes, and then changes back to the original reading on operation of the switch again. If the reading did
not change, then the switch is likely to be connected in the Neutral. ↔ ( Not good! ) ↔ With a little foresight this could be carried out at the same time as the continuity test. The only difference being, for radial circuits every point must be tested.
The main benefit with this is it allows you to conduct (2 ) tests at the same time, polarity and R1 + R2.

( 2392-10 -&- ↔ for radial circuits every point must be tested. )

Method 2
This method, like wise is similar to test 2 of the continuity test, we simply use a wander lead as the return lead.
There is little use for this method, within the polarity test. Method 1 is less clumsy, and is far more flexible and useful.
(see figure 2).

A Note on radial socket outlets
We have covered ring final circuits, but radial final circuits involving sockets can prove to be little more involved.
Why ? You may ask, well simply because doing a polarity check using method 1, will not uncover a phase to cpc reversal. If the phase and cpc were reversed at the socket, the instrument will still
provide a reading (Figure 3). It will however tell you if you have a phase to neutral reversal ( you wouldn’t have a reading at the socket ). So what can we do to expose a phase – cpc reversal? We can simply link the phase and neutral together at the board, and put our instrument across phase and neutral at the socket, if the cpc and
phase have been reversed, then no reading will be recorded on the instrument. This one takes a while to get your head around ,

Test Method 1 : figure 1

1. Create a temporary link between the phase and the CPC within the consumer unit
2. At each point on the circuit, connect the low resistance ohmmeter to the phase and CPC
3. Operate the switches

Test Method 2 : figure 2).
1. Connect the wander lead to the phase conductor at the furthest point at each point on the circuit ,
2. Connect the low resistance ohmmeter to the phase conductor within the consumer unit
3. Operate the switches

Figure 3 :
Reversed Phase and CPC at socket outlet

 

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Re: Section - 301- Questions - Testing ,

Passing an ECS Health and Safety Assessment is ↔ Compulsory ↔
→→→ For all you Chaps Renewing you ( J.I.B. Card ) ←←← 13 . 11 . 09

SOLAR PHOTOVOLTAIC :


SOLAR ELECTRICITY
The panels produce direct current (DC) which is converted to alternating current (AC) by an inverter so it can be used by appliances in the home. These systems can either be connected to the national electricity grid, or connected to a battery.

THE GENERAL INFORMATION ON SOLAR PHOTOVOLTAIC

“Photovoltaic” is a marriage of two words: “photo”, from Greek roots, meaning light, and “voltaic”, from “volt”, which is the unit used to measure electric potential at a given point.

Photovoltaic systems use cells to convert solar radiation into electricity. The cell consists of one or two layers of a semi-conducting material. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. The greater the intensity of the light, the greater the flow of electricity is.

The most common semi conductor material used in photovoltaic cells is silicon, an element most commonly found in sand. There is no limitation to its availability as a raw material as silicon is the second most abundant material in the Earth’s mass.

A photovoltaic system therefore does not need bright sunlight in order to operate. It can also generate electricity on cloudy days. Due to the reflection of sunlight, slightly cloudy days can even result in higher energy yields than days with a completely cloudless sky.

The power output of a solar array is measured in watts or kilowatts. In order to calculate the typical energy needs of the application, a measurement in watt-hours, kilowatt-hours or kilowatt-hours per day is often used. A common rule of thumb is that average power is equal to 20% of peak power, so that each peak kilowatt of solar array output power corresponds to energy production of 4.8 kWh per day ( 24 hours x 1 kW x 20% = 4.8 kWh )

Fault Currents :

Fault currents arise as a result of a fault in the cables or equipment , there is a sudden increase in current , perhaps 10 or 20 times the cable rating ,
The current being limited by the impedance of the supply , the impedance of the cables , the impedance of the fault and the impedance of the return path , the current is normally of short duration ,

Overload Currents :

Overload Currents do not arise as a result of a fault in the cable or equipment , they arise because the current has been increased by the addition of further load ,
Overload protection is only required if overloading is possible , it would not be required for a circuit supplying a fixed load , but fault protection is required except in exceptional circumstances ( 434.5.1 )

Basic fault finding of fluorescent fittings :

The following checks are recommended to be carried out when checking any suspected faulty fitting.
All checks, apart from 2., should be carried out with the mains supply to the fitting disconnected.

1. Check the ballast / lamp combination
• Ensure the ballast is suitable for the lamp/s being used.
• If the combination is found to be incorrect then it should be determined whether it is actually the ballast or the lamp that is the incorrect item.

2. Check that there is mains supply to the fitting.
• Ensure that the supply not only comes to the fitting, but also goes to the ballast.
• Remember to measure the voltage between Live and Earth, Live and Neutral, and Neutral and Earth.

3. Check that the lamps are in good condition.
• Even new lamps can be faulty.
• Measure each lamp cathode and check for the correct resistance reading.
• The resistance reading should be between 1 - 10Ω, depending on the lamps used.

4. Check that the lamps are inserted into the lamp holders correctly.
• Poor connections will give intermittent operation.

5. Check the wiring of the fitting.
• Are the supply wires connected correctly?
• Are the control wires connected correctly (if used)?
• Check that there are no loose connections.
• Are the lamp wires connected correctly?
• Check this against the wiring diagram on the ballast.
• Check the connections at the lamp holders as well as at the ballast.
• Are the ’ Line ’ and ’ Neutral ’ wires connected correctly?

If the above checks have been carried out and a fault is still evident, replace the ballast.

 

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“ Possible Causes Of RCD Tripping :

Faulty appliance – unplug all electrical appliances, does the RCD reset OK ? If the RCD resets OK plug the appliances back in one at a time. Reset the RCD as you plug each appliance back in to find the faulty appliance.

Electricity can kill – if turning an RCD off to work on a circuit always double check that there is no power in the circuit: ( Lock off )

Incorrect RCD current rating – RCDs have ‘current ratings’ similar to fuses. The current rating is the current that trips an RCD. The current rating of the RCD could be too low.

Poor quality RCD – poor quality RCDs can trip when they shouldn’t.

Items with motors or pumps starting – many items with motors or pumps, for instance showers and pond pumps, cause momentary electrical spikes that are big enough to trip RCDs.

Older washing machines – aging washing machine heating elements can cause momentary electrical spikes that are big enough to trip RCDs.

Certain wash cycle phases – some cycles of the washing machine, for instance the spin cycle, can cause momentary electrical spikes that are big enough to trip RCDs.

Certain dishwasher cycles – some parts of the dishwasher cycle draw a lot of current, a faulty component, for instance the motor, can trip an RCD.

Overloading a washing machine – too many items in a washing machine can cause certain wash cycles, for instance the spin cycle, to trip an RCD.

Fridges and freezers cooling – the fridge or freezer cooling motor starting.

Turning a sun bed on – a sun bed uses a lot of electrical power, the surge in electrical power can trip an RCD.

Turning an heating element on after a long time of being off – moisture in heating elements can trip an RCD, for instance in a sun bed or electric fire. Try resetting the RCD a few times so that the heating element can cause the moisture to evaporate.

Pond pump faulty – pond pumps sometimes have to ‘work very hard’– for instance when they have ‘digested’ part of a plant from the pond. Check your pond pump for blockages.

Moisture in outside electrical distribution boxes – remove the supply and dry the distribution box. Check the weather seals have not perished.

Moisture in outside electrical sockets – remove the supply and dry the electrical socket. Check the weather seals have not perished.

Ice maker on a fridge – a faulty ice maker on a fridge can cause ‘nuisance’ RCD tripping.

De-frost timer on a fridge or freezer – a faulty defrost element on a fridge or freezer can cause ‘nuisance’ RCD tripping.

Central heating elements – faulty heating elements can cause an RCD to trip when they are turned on by a timer.

Moisture in wiring – moisture in the electrical wiring is a common cause of RCD trips. Have you just emptied a bath? Taken a shower ? Is it raining – rain can get into the electrical wiring under the floors or in the loft.

After unplugging all appliances, or turning them off, see if the RCD will reset. If the RCD will reset, the fault is with one of the appliances; if the RCD trips again the fault is with the electrical circuit.

Plug each appliance in one at a time. After plugging the appliance in, or turning an appliance on, reset the RCD; keep plugging the appliances in, and resetting the RCD, until the RCD trips.

Connecting the appliances one at a time, and resetting the RCD in-between, shows the homeowner which appliance is causing the RCD to trip. The homeowner should repair, or replace, the faulty appliance.

Plugging each appliance in one at a time is not a100% guarantee of finding the faulty appliance; it is the best way, but not a 100% guarantee. Certain ‘cause\effect’ situations can suggest a, say, faulty kettle when the real problem is, say, a faulty cooker.

1) Are any electrical circuits working?
2) Has something simple just triggered the switch?
3) A light bulb blowing or light switch arcing can sometimes trip the fuse?

9 times out of 10, an RCD tripping will be in response to something that you (or your family) has just done.
1 out of 10 times, it will be as a result of either physical failure of the device or a build up of fault current which eventually tips the balance.

“ Recessed Light (‘Down Light’) Problems “

* Recessed lights (down lights) have many different wattage ratings. Is the bulb wattage rating correct? Compare the problem bulb, or bulbs, with bulbs that work OK – are they the same?

* Is something covering the bulb housing, for instance loft insulation? Overheating causes many different problems.

* Lights generate a lot of heat – if the lights are ‘recessed’ ensure there is enough space for the heat to dissipate.

* Connect the electrical power input wire to the switch output to bypass the switch – if the light works the switch is at fault.

What Can Go Wrong With A Light Switch

* Loose wiring in switch.

* Switch mechanism broken.

* Damaged wiring.

* Bare wires touching the switch housing.

Symptoms Of A Broken Light Switch With Possible Causes

* Light switch does not work:
* Loose wiring in switch.
* Broken switch.
* Poor connection to light switch terminals.
* Bare wires touching the switch housing.

* Light switch ‘buzzing’ or discoloured:
* Loose wiring in switch.
* Internal arcing.
* Bare wires touching the switch housing.

* Switch hot:
* Loose wiring in switch.
* Bare wires touching the switch housing.

* Lights flickering:
* Loose wiring in switch.
* Poor connection to light switch terminals.
* Bare wires touching the switch housing.

 

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Measures of protection against fire risk with RCDs

RCDs are very effective devices to provide protection against fire risk due to insulation fault. This type of fault current is actually too low to be detected by the other protection (overcurrent, reverse time). For TT, IT TN-S systems in which leakage current can appear, the use of 300mA sensitivity RCDs provides a good protection against fire risk due to this type of fault. An investigation has shown that the cost of the fires in industrial and tertiary buildings can be very great. The analysis of the phenomena shows that fire risk due to electricity is linked to overheating due to a bad coordination between the maximum rated current of the cable (or isolated conductor) and the overcurrent protection setting. Overheating can also be due to the modification of the initial method of installation (addition of cables on the same support). This overheating can be the origin of electrical arc in humid environment. These electrical arcs evolve when the fault current-loop impedance is greater than 0.6 Ωand exist only when an insulation fault occurs. Some tests have shown that a 300mA fault current can induce a real risk of fire

RCDs are very effective devices to provide protection against fire risk due to insulation fault because they can detect leakage current (ex : 300 mA) which are too low for the other protections, but sufficient to cause a fire

Protection when exposed conductive parts are not connected to earth

(In the case of an existing installation where the location is dry and provision of an earthing connection is not possible, or in the event that a protective earth wire becomes broken).
RCDs of high sensitivity (y 30 mA) will afford both protection against indirect-contact hazards, and the additional protection against the dangers of direct-contact.

Determination of voltage drop

The impedance of circuit conductors is low but not negligible: when carrying load current there is a voltage drop between the origin of the circuit and the load terminals. The correct operation of a load (a motor, lighting circuit, etc.) depends on the voltage at its terminals being maintained at a value close to its rated value. It is necessary therefore to determine the circuit conductors such that at full-load current, the load terminal voltage is maintained within the limits required for correct performance.
methods of determining voltage drops, in order to check that:

* They comply with the particular standards and regulations in force
* They can be tolerated by the load
* They satisfy the essential operational requirements

Maximum voltage drop

Maximum allowable voltage-drop vary from one country to another. Typical values for LV installations are given below
A low-voltage service connection from a LV pubic power distribution network , lighting 3% - Other uses ( Heating & Power 5% )
Consumers MV/LV substation supplied from a public distribution MV systems , 6% / 8%

Maximum voltage-drop between the service-connection point and the point of Utilization ,
These voltage-drop limits refer to normal steady-state operating conditions and do not apply at times of motor starting, simultaneous switching (by chance) of several loads, etc. as mentioned in Chapter A Sub-clause 4.3 (factor of simultaneity, etc.). When voltage drops exceed the values , larger cables (wires) must be used to correct the condition.

The value of 8%, while permitted, can lead to problems for motor loads; for example:

* In general, satisfactory motor performance requires a voltage within ± 5% of its rated nominal value in steady-state operation,

* Starting current of a motor can be 5 to 7 times its full-load value (or even higher). If an 8% voltage drop occurs at full-load current, then a drop of 40% or more will occur during start-up. In such conditions the motor will either:

* Stall (i.e. remain stationary due to insufficient torque to overcome the load torque) with consequent over-heating and eventual trip-out

* Or accelerate very slowly, so that the heavy current loading (with possibly undesirable low-voltage effects on other equipment) will continue beyond the normal start-up period

* Finally an 8% voltage drop represents a continuous power loss, which, for continuous loads will be a significant waste of (metered) energy. For these reasons it is recommended that the maximum value of 8% in steady operating conditions should not be reached on circuits which are sensitive to under-voltage problems ,

Legal basis

In England and Wales, the Building Regulations (Approved Document: Part P) require that domestic electrical installations are designed and installed safely according to the "fundamental principles" given in British Standard BS-7671 Chapter 13. These are very similar to the fundamental principles defined in International Standard IEC – 60364-1 and equivalent national standards in other countries. Accepted ways for fulfilling this legal requirement include

* the rules of the IEE wiring regulations ( BS–7671 ), colloquially referred to as "the regs" (BS 7671: 2008, 17th Edition).;

* the rules of an equivalent standard approved by a member of the EEA (e.g., DIN/VDE 0100);

* guidance given in installation manuals that are consistent with BS 7671, such as the IEE On-Site Guide and IEE Guidance Notes Nos 1 to 7.

Installations in commercial and industrial premises must satisfy various safety legislation, such as the Electricity at Work Regulations 1989. Again, recognized standards and practices, such as BS 7671 "Wiring Regulations", are used to help meet the legislative requirements.

Commissioning Certificate

BS-5266 and the European Standard both require written declarations of compliance to be available on site for inspection. These consist of
1. Installation quality.
IEE regulations must have been conformed with and non-maintained fittings fed from the main circuit of the normal lighting system, as required in BS 5266

2. Photometric performance.
Evidence of compliance with light levels has to be supplied by the system designer.

3. Declaration of a satisfactory test of operation.
A log of all system tests and results must be maintained. System log books, with commissioning forms, testing forms and instructions should be provided by the installer.
On completion of the installation of the emergency lighting system, or part thereof, a completion
certificate should be supplied by the installer to the occupier/owner of the premises. The Building Control Department should insist upon a copy of this certificate which will be retained with the Building Regulations Authority.
Maintenance
Finally, to ensure that the system remains at full operational status, essential servicing should be defined. This normally would be performed as part of the testing routine, but in the case of consumable items such as replacement lamps, spares should be provided for immediate use.

Routine inspections and tests

Where national regulations do not apply, the following shall be met.
Because of the possibility of a failure of the normal lighting supply occurring shortly after a period of testing of the emergency lighting system or during the subsequent recharge period, all full duration tests shall wherever possible be undertaken just before a time of low risk to allow for battery recharge. Alternatively, suitable temporary arrangements shall be made until the batteries have been recharged.
The following minimum inspections and tests shall be carried out at the intervals recommended below. The regulating authority may require specific tests.
Daily
Indicators of central power supply shall be visually inspected for correct operation.
NOTE. This is a visual inspection of indicators to identify that the system is in a ready condition and does not require a test of operation.
Monthly
If automatic testing devices are used, the results of the short duration tests shall be recorded.
For all other systems the tests shall be carried out as follows:
a) Switch each luminaire and each internally illuminated exit sign to emergency mode so it uses the battery. This simulates a failure of the supply of the normal lighting and continue for a period sufficient to ensure that each lamp is illuminated.
At the end of this test period, the supply to the normal lighting should be restored and any indicator lamp or device checked to ensure that it is showing that the normal supply has been restored.
NOTE. The period of simulated failure should be sufficient for the purpose of this clause whilst minimising damage to the system components e.g. lamps. During this period, all luminaire's and signs shall be checked to ensure that they are present, clean and functioning correctly.
b) For central battery systems, the correct operation of system monitors shall be checked.
c) For generating sets, refer to the requirement of ISO 8528-12.
Annually
If automatic testing devices are used, the results of the full rated duration test shall be recorded.
For all other systems the following tests made:
a) each luminaire and internally illuminated sign shall be tested as per monthly test but for its full rated duration in accordance with the manufacturer's information;
b) the supply of the normal lighting shall be restored and any indicator lamp or device checked to
ensure that it is showing that normal supply has been restored. The charging arrangements should
be checked for proper functioning;
c) the date of the test and its results shall be recorded in the system logbook;
d) For generating sets, refer to the requirements of ISO 8528-12.

 

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Currently the national safety standard for electrical installation work in the UK is British Standard 7671 – Requirements for
Electrical Installations. The IEE Wiring Regulations are a code of practice for ensuring safe electrical installations.

Although the IEE Wiring Regulations have no statutory force in the UK, they are referred to as a means of demonstrating compliance with relevant legislation, such as the Electricity at Work Act (1989) and the Building Regulations.

Fault Protection

Protection against electric shock under single-fault conditions. Note: For low voltage installations, systems and equipment,
fault protection generally corresponds to protection against indirect contact, mainly with regard to failure of basic insulation.
Indirect contact is ‘contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions’.

Section 701 concerns locations containing a bath or shower. It is now a requirement under 701.411.3.3 that additional
protection shall be provided for all circuits of the location by the use of one or more RCDs, again, with an operating
current not exceeding 30mA, reference Regulation 415.1.1. As well as items such as electric towel rails and electric showers, this regulation also applies to lighting. Although all of the aforementioned areas require RCD protection, the requirements of Regulation 314.1, Division of Installation, need to be taken into account, when designing and installing the circuit protective arrangements. 314.1
states that every installation shall be divided into circuits as necessary to:

a. Avoid hazards and minimise inconvenience in the event of a fault

b. Take account of danger that may arise from the failure of a single circuit such as a lighting circuit

c. Reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation

 

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Functional switches are required to be suitable for the most onerous duty intended (rated to carry the highest load on that circuit), and should be selected to have a utilization category appropriate for the type of load being switched.

Isolation of a luminaire

The objective of isolation is to enable electrically skilled persons to carry out work on, or adjacent to, parts which would otherwise be live e.g. for a luminaire, replacing a faulty ballast or ignitor.

Electrical Faults – where do they occur ?

Electrical Faults may occur in electrotechnical systems at the following places ,
a) The wiring system ,
b) At cable terminations ,
c) Within accessories, switchgear , contactors and controls ,
d) Within instrumentation and metering equipment ,
e) At protective devices ,
f) At luminaires ,
g) in flexible cables and cords ,
h) in electrical components ,
each of these potential fault situations ;

Electrical Faults in the wiring system :
The electrical designer will choose a wiring system which meets the needs of the client and any relevant regulations , part 5 of the IEE Regulations deals with the selection and erection of equipment and the designer must choose a wiring systems which complies ,

* The wiring system must be suitable for the installed conditions such as temperature , presence of water , vibration , corrosion and solar radiation ,

The electrician must install the wiring system competently and in compliance with the IEE Regulations . for ;
Buried cables must have mechanical protection , and underground cables must be buried at sufficient depth to prevent future damage ,
Cables installed in timber joist must be at least 50mm from the top and bottom of the joist , and the installed wiring system must not reduce the safety of the building structure ,

A suitable wiring system , correctly installed will cause few problems in the future , it is where the human hand has been involved
At each end of the wiring systems there future problems most often occur ,

POWER CIRCUITS :
Showers
Often forming part of modern installations is the electric shower. With sizes now reaching 11kw, it is vitally important that we calculate the correct cable size. Remember the power formula ? An 11 kW shower can draw currents up to 48A !

Cookers
Ovens and cooking devices :
An electric cooker can often have enough parts (top oven, bottom oven, grill etc.) to produce a large amount of current. Although we can apply diversity from the On Site Guide, modern ovens can have a large amount of features that must be taken into account when designing the circuit.

Water heaters :
As a general rule, any water heater over 15 litres should be fed by an independent circuit. Again, calculations should be made regarding the power consumption of the heating element although in most instances, it will be fed by a 16A protective device and 2.5mm2 cable.

OTHER CIRCUITS :
Fire alarm
Introduced into the Building Regulations, specifically, Part B: Fire Safety, was the provision of a separate circuit for a fire alarm. It is thought that a separate circuit will not be isolated for any period of time hence the need to remove it from circuits such as lighting or socket outlet circuits.

DOMESTIC FINAL CIRCUIT ARRANGEMENTS

The IEE Regulations, specifically the On Site Guide, takes a lot of work out of the design of a domestic installation for a typical installer. This combined with the Building Regulations gives us a quick and easy platform to determine the requirements.

RING AND RADIAL SOCKET OUTLET CIRCUITS
The On Site Guide gives us 3 options for the installation of socket outlets. These can be found in Appendix 8 of the On Site Guide and can be simplified to the following: O/S/G , 158 , Table 8A
A1 : Ring : 30 or 32A : 100m2
A2 : Radial : 30 or 32A : 75m2
A3 : Radial : 20A : 50m2

CITY AND GUILDS 2393 - CERTIFICATE IN THE BUILDING REGULATIONS FOR ELECTRICAL INSTALLATIONS IN DWELLINGS

The City and Guilds have also launched qualifications around the Building Regulations known as the 2393-10
The idea behind this qualification is to enable the allied trades and existing electricians working in the domestic environment to gain an understanding on how the Building Regulations impacts on electrical installations.
It is a 20 question multiple choice paper completed within 40 minutes and covers the following:
• Building Regulations
• Building Work
• Approved Documents
• Building Control
• Compliance with Approved Documents A to M

Part P does not apply in the case of all buildings. It applies to all fixed electrical installations after the suppliers’ meter in buildings or parts of buildings comprising:

• Dwellings
• Dwellings and business premises such as shops and public houses that have a common supply
• Common access areas in blocks of flats such as corridors and staircases but not lifts shared amenities in blocks of flats, such as laundries and gymnasiums.
While Approved Documentation ‘P’ applies to all electrical installation work in dwellings, it is not necessary to notify building control bodies in the following circumstances:

• The electrical installation work is to be undertaken by a ‘Competent Person’ and self certificated*
• When electrical installation work is 'Minor Work' and is not contained within the kitchen or special location and does not involve a special installation

• Competent persons registered enterprises (Competent Persons Scheme)

* Clarify this with your local Building Control before commencing work. Although Part P was designed to enforce standards and increase safety, many council offices simply do not understand the implications of the document and merely insist you are part of a competent persons scheme. This is not true but you do need to notify before you begin work on an installation.

* What types of mechanical protection provide sufficient protection against penetration by nails, screws and the like :

- As an example, steel of 3 mm minimum thickness is generally considered to provide sufficient mechanical protection, except where shot-fired nails are likely to be used. 522.6.6 / 522.6.8

* Do ‘meter tails’ concealed in walls or partitions need to be protected in accordance with Regulations 522.6.6 and/or 522.6.8 :

- Yes. Meter tails concealed in a wall or partition at a depth of less than 50 mm from a surface must be protected in accordance with Regulation 522.6.6. Also, irrespective of the depth from a surface, meter tails concealed in a wall or partition having internal metallic parts (except nails and screws, etc) are subject to the requirements of Regulation 522.6.8. ( 522.6.6, 522.6.8 314.1, 314.2 )

- However, additional protection for meter tails by means of an RCD is not an acceptable option in respect of Regulation 522.6.7 (which in consequence rules out reliance on 522.6.6(v), routing in the ‘safe zones’ alone), or in respect of Regulation 522.6.8(v). Also, for TT systems, the only option remaining is to provide suitable mechanical protection (that is, to comply with Regulations 522.6.8(iv) and/or 522.6.6(iv) as appropriate).

* Does boiler pipework need to have additional equipotential bonding for electrical safety reasons :

- There is no specific requirement in the Regulations for boiler pipework to be supplementary bonded. However, such bonding may be called for in the boiler manufacturer’s instructions, in which case BS 7671 requires those instructions to be followed (Regulation 510.2 refers). Any stated requirement for additional bonding that is considered to be unnecessary should be queried with the manufacturer concerned, and amended installation instructions requested. ( 411.3.3 )

* I am still working on an electrical installation that was designed to the 16th Edition. To which Edition should the installation be inspected, tested, verified and certificated :

- An installation designed and installed to the 16th Edition should be inspected, tested, verified and certificated to that Edition.

* Is an RCD main switch (such as a 100mA time-delayed device) still required in the consumer unit of a new domestic installation forming part of a TT system :

For a domestic installation complying with the 17th Edition where all the final circuits are RCD-protected, an RCD main switch is no longer required, provided that the consumer unit is of all insulated construction.

* Does the device that has to be provided for switching off a bathroom extract fan for mechanical maintenance need to be located adjacent to the fan :

- No, but the device does need to be so placed and marked as to be readily identifiable and convenient for the intended use ( 537.3.2.4 )

* Does the R1 + R2 test confirm& the correct polarity of a radial circuit :

- No, not on its own. Whilst the test can provide an indication of polarity, it needs to be combined with inspection and further testing as required by Part 6 of BS 7671: 2008 ( 611.3, 612.6 )

* Appendix 15 of BS 7671: 2008 gives advice on ring final circuits and sharing/spreading the load around the circuit. Item (iii) suggests that cookers, ovens and hobs over 2 kW should be on their own dedicated circuit. Why can’t ovens of less than 3 kW be connected to a ring final circuit via a suitable connection point such as a socket-outlet or fused connection unit :

- Appendix 15 is intended to give guidance only. Such connection is not prohibited, provided that no part of the ring final circuit will be overloaded as a result. ( 433.1.5 )

 

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* Is it necessary to verify voltage drop during initial verification :

- Verification of voltage drop is not normally required unless there is considered to be a voltage drop problem. ( 612.14 )

* Considering Regulations 134.1.1 and 510.2 which require equipment to be installed in accordance with instructions provided by the manufacturer, are installers now required to check torque settings for connection tightness at consumer units where these are manufacturers instructions.

- Yes. It is necessary to check that all connections are tight, and any specific installation instructions must also be followed.

* In a location containing a shower, what is the horizontal limit of zone 1 for showers without a basin :

- The limit of zone 1 horizontally is 1.2 m from the centre point of the fixed water outlet (the end of the rigid pipe of the fixed water installation) on the wall or ceiling, irrespective of whether the shower head is fixed or on the end of a flexible hose. Beyond zone 1, the general rules of BS 7671 apply, including Regulation 512.2 concerning external influences. In particular, the IP rating of any electrical equipment must be adequate. ( 701.32.4 512.2 )

* Regulation 560.7.7 requires cables for safety circuits, other than metallic screened fire-resistant cables, to be adequately and reliably separated from other circuit cables. In addition to mineral insulated cables, what cables would be exempted from this separation requirement : ( 560.7.7 )

- Soft-skinned cables to BS 7629-1: 2008 would be exempted from the separation requirements as they have a metallic screen and their survival in a fire has been tested in accordance with BS EN 50200. However, cables to BS 8436: 2004 would not be exempted as the product standard does not require their fire resistance to be tested. Irrespective of the above, BS 5839-1 recommends that, for a fire detection and alarm system complying with that standard, the circuits of fire alarm systems should be segregated from the cables of other circuits to minimize the potential for those other circuits to cause malfunction of the fire alarm system.

* As the designer of an installation, am I allowed to rely on the RCD element of an RCBO to provide for fault protection in order to allow for loop impedance values greater than given in Table 41.3 :

- Yes, so long as all the other applicable requirements of the 17th Edition are met, including those for protection against overload and short circuit. ( 411.4.4 411.4.5 411.4.9 )

* Are there any particular requirements relating to the mounting height or location of consumer units for electrical installations in new dwellings :

- The provision of access to consumer units is not specifically covered by Building Regulations or BS 7671. However, consumer units need to be so located as to enable reasonable access by the users, including for the purpose of testing the RCDs at regular intervals, and in case of emergency. ( 132.12 341.1 513.1 )

- BSI Draft for development DD 266: 2007 – Design of accessible housing: Lifetime homes – Code of practice, explains how, by following the principles of inclusive design, general needs housing can be made sufficiently flexible and convenient to meet the existing and changing needs of most households, and so give disabled and older people more choice over where they live.
Amongst other things, the code of practice recommends that meters and consumer units should be mounted 1200 mm to 1400 mm from the floor so that the readings and switches can be viewed by a person standing or sitting, and should be positioned to be accessible.

* What is the correct sequence for testing RCDs :

- Preferably, RCDs should be tested in the sequence of: x1 I∆n , x5 I∆n (if required for additional protection), followed by x0.5 I∆n and then finally the test button trip.

- However, some automated test instruments test in the sequence of: x0.5 I∆n followed by the x1 I∆n test, and then x5 I∆n test (if required for additional protection).

- In any case, the test button should be operated last in the sequence

Note: Unless otherwise indicated, all references to ‘RCD’ in this section relate to residual current devices having a rated residual operating current ( I∆n ) not exceeding 30 mA and an operating time not exceeding 40 ms at a residual operating current of 5 I∆n , provided as additional protection in the event of failure of the provision for basic protection and/or the provision for fault protection or carelessness by users (Regulation 415.1.1)

 

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Inspection and Testing of Electrical Equipment : PAT !!!


The following ten questions will indicate the scope and level of background knowledge required, for which it is strongly advised that you should be able to achieve at least 80% correct answers.

1. Place the appropriate number in the box opposite each of the following electrical parameters to indicate the letter by which each is designated:

(a) current (b) voltage (c) resistance (d) electric power


1 – A ; 2 – C ; 3 – I ; 4 – P; 5 − R ; 6 − U ; 7 – V ; 8 - W


(2) Place the appropriate numbers in the boxes opposite each of the following electrical parameters to indicate (i) its basic unit of measurement and (ii) the letter or symbol by which that unit is designated:
………….…………………… (i) ……….. …………. (ii)
(a) current …………………… ( ) ……….. …………. ( )
(b) voltage …………………… ( ) ……….. …………. ( )
(c) resistance ………………….( ) ……….. …………. ( )
(d) electric power ……………. ( ) ……….. …………. ( )

(i) 11 – watt; 12 – hertz; 13 – ohm; 14 – farad; 15 – volt; 16 – ampere(amp)
(ii) 21 – A; 22 – O; 23 – R; 24 – U; 25 – V; 26 – W; 27 - Ω; 28 - α

A) ↔ 2. (a) (i) – 16 (ii) – 21 (b) (i) – 15 (ii) – 25 (c) (i) – 13 (ii) – 27 (d) (i) – 11 (ii) – 26

(3) 100mA is the same as:
(a) 10 A
(b) 1 A
(c) 0.1 A ←
(d) 0.01 A

(4) 2 MΩ is the same as:
(a) 0.002 Ω
(b) 0.02 Ω
(c) 2,000 Ω
(d) 2,000,000 Ω ←

(5) 2mΩ is the same as:
(a) 0.002 Ω ←
(b) 0.02 Ω
(c) 2,000 Ω
(d) 2,000,000 Ω

(6) A portable appliance is fitted with a 5 m cord for which the resistance of the protective conductor is 26 mΩ/m. The total resistance of the protective conductor is:
(a) 26 mΩ
(b) 52 mΩ
(c) 130 mΩ ←
(d) 260 mΩ

(7) The protective conductor resistances of two extension leads are 95 mΩ and 75 mΩ respectively. When connected together in series the combined resistance is:
(a) 0.02 ohms
(b) 0.085 ohms
(c) 0.17 ohms ←
(d) 0.34 ohms

(8) An electrical appliance is rated 230 V, 920 W. When connected to a 230 V supply the load current should be:
(a) 0.25 A
(b) 0.4 A
(c) 2.5 A
(d) 4 A ←

(9) The core colours for the phase, neutral and protective conductors of a 3-core appliance cord should be respectively:
(a) red, black and green
(b) red, black and green/yellow
(c) brown, blue and green
(d) brown, blue and green/yellow ←

(10) The nominal voltage of a single-phase mains electricity supply is:
(a) 230 V d.c.
(b) 230 V a.c. ←
(c) 240 V d.c.
(d) 240 V a.c.

(11) Which one of the following does NOT specifically comprise a user check:
(a) confirming that the plug is correctly connected ←
(b) confirming that the flexible cable is secure in the plug anchorage
(c) confirming that the equipment is suitable for the job
(d) confirming that there are no signs of overheating at the socket outlet

(12) An item of class I equipment incorporating unearthed metal separated from live parts by basic insulation and earthed metal is subjected to several earth continuity tests. The results are found to be inconsistent. This is most likely to be as a result of:
(a) a variation in the earth fault loop impedance of the final circuit providing the mains supply to the portable appliance tester
(b) the unearthed metal being in casual contact with earthed metal ←
(c) variation in the supply frequency
(d) the earthed metal changing temperature

(13) When undertaking a protective conductor/touch current measurement on a 2 kW
Class I heating appliance the maximum permitted current is:
(a) 0.25mA
(b) 0.75mA
(c) 1.5mA ←
(d) 3.5mA

(14) The test voltage for an electric strength test undertaken by the manufacturer on the
basic insulation of IT equipment conforming to BS EN 60950 is:
(a) 230 V
(b) 1000 V
(c) 1500 V ←
(d) 3000 V

(15) A low resistance ohmmeter is used to check the polarity of a 3-core extension lead.
The end-to-end resistance measurements are:
Plug phase pin to socket phase connection – open circuit
Plug neutral pin to socket neutral connection – 0.15 Ω
Plug protective conductor pin to socket protective conductor connection – open circuit
Plug phase pin to socket neutral connection – open circuit
Plug phase pin to socket protective conductor connection – 0.15 Ω
Plug protective conductor pin to socket neutral connection – open circuit
Plug protective conductor pin to socket phase connection – 0.15 Ω

These test results show crossed connections between the:
(a) phase and neutral conductors
(b) phase and protective conductors ←
(c) phase, neutral and protective conductors
(d) neutral and protective conductors

A/Q
1. (a) – 3 (b) – 6 (c) – 5 (d) – 4

2. (a) (i) – 16 (ii) – 21
(b) (i) – 15 (ii) – 25
(c) (i) – 13 (ii) – 27
(d) (i) – 11 (ii) – 26

3. (c) 4. (d) 5. (a) 6. (c) 7. (c) 8. (d) 9. (d) 10. (b) 11. (a) 12. (b) 13. (c) 14. (c) 15. (b)

Revision on motors :
1) looking for R.P.M :
Ns = 60 x f ----------- p ( f = 50 Hz : p = 10 = 5 pair of poles : Ns =( ? ) R.P.M ←←
( 60 x 50 ----------- 5 : Ans ↔ ( 60 x 50 = 3000 ÷ 5 = 600 rpm ) *

2) looking for frequency :
Ns = 60 x f ----------- p ( Ns = 1800 rpm , p = 4 = 2 pair , f = ( ? ) Hz ←←
f = Ns x p ----------- 60 Ans ↔ ( 1800 x 2 ÷ 60 = 60 Hz ) *

3) looking for pair = poles :
Ns = 60 x f ----------- p ( f = 50 Hz : Ns = 750 rpm : p = ( ? ) pair of poles ←←
( p = 60 x f ----------- Ns Ans ↔ ( 60 x50 ÷ 750 = 4 *
↔ p = 4 pair of poles : ( Number of pole = 2 x 4 = 8 ) *

4) looking for RPM :
Ns = 60 x f ----------- p ( f = 50 Hz : p = 10 = 5 pair / poles : Ns = ( ? ) RPM ←←
60 x 50 ----------- 5 Ans ↔ ( 60 x 50 = 3000 rpm *

Level 3 Electro-Technical : Exam Questions Not Multiple Choice Questions with Answers :

Questions
1) A resistor of 28_ is connected to a inductor of 12mH and a capacitor of 24μF. Calculate
the impedance presented to the 50Hz supply.
2) A resistor of 38_ is connected to a inductor of 124mH and a capacitor of 100μF.
Calculate the impedance presented to the 50Hz supply.
3) A resistor of 12k_ is connected to a inductor of 56.92mH and a capacitor of 178μF.
Calculate the impedance presented to the 50Hz supply.
4) A resistor of 164_ is connected to a inductor of 84mH and a capacitor of 18μF. Calculate
the impedance presented to the 50Hz supply.
5) A resistor of 216_ is connected to a inductor of 136mH and a capacitor of 124μF.
Calculate the impedance presented to the 50Hz supply.
6) A transformer has a rated power of 15kVA and a power factor of 0.9 and the losses are
200 Watts. Calculate the overall efficiency.
7) A transformer has a rated power of 8kVA and a power factor of 1 and the losses are
1800 Watts. Calculate the overall efficiency.
8) A transformer has a rated power of 1kVA and a power factor of 0.75 and the losses are
100 Watts. Calculate the overall efficiency.
9) A transformer has a rated power of 24kVA and a power factor of 0.95 and the losses are
1400 Watts. Calculate the overall efficiency.
10) A transformer has a rated power of 12kVA and a power factor of 0.85 and the losses are 600 Watts. Calculate the overall efficiency.

 

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Answers
Two equations are used, depending upon the values of XL and XC:
If XL is larger than XC, then: Z = √ (R2 + (XL- XC)2
If XC is larger than XC, then: Z = √ (R2 + (XC- XL)2
1) A resistor of 28_ is connected to a inductor of 12mH and a capacitor of 24μF. Calculate
the impedance presented to the 50Hz supply.
XL = 2πfL = 3.77_, XC = 1 / (2πfC) = 132.63_, Z = √ (R2 + (XC- XL)2 = 131.87_
2) A resistor of 38_ is connected to a inductor of 124mH and a capacitor of 100μF.
Calculate the impedance presented to the 50Hz supply.
XL = 2πfL = 38.96_, XC = 1 / (2πfC) = 31.83_, Z = √ (R2 + (XL- XC)2 = 38.66_
3) A resistor of 12k_ is connected to a inductor of 56.92mH and a capacitor of 178μF.
Calculate the impedance presented to the 50Hz supply.
XL = 2πfL = 17.88_, XC = 1 / (2πfC) = 17.88_, In this case XL=XC, so Z=R = 12k_
4) A resistor of 164_ is connected to a inductor of 84mH and a capacitor of 18μF. Calculate
the impedance presented to the 50Hz supply.
XL = 2πfL = 26.39_, XC = 1 / (2πfC) = 176.84_, Z = √ (R2 + (XC- XL)2 = 222.56_
5) A resistor of 216_ is connected to a inductor of 136mH and a capacitor of 124μF.
Calculate the impedance presented to the 50Hz supply.
XL = 2πfL = 42.73_, XC = 1 / (2πfC) = 25.67_, Z = √ (R2 + (XL- XC)2 = 216.67_
6) A transformer has a rated power of 15kVA and a power factor of 0.9. and the losses are
200 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 15kVA x 0.9 = 13.5kW
Output power = Input power - losses
Output power = (15kVA X 0.9) - 200 = 13500 - 200 = 13.3kW
Efficiency = (Output/input) x 100%, n = (13300/13500) x 100 = 98.52%
7) A transformer has a rated power of 8kVA and a power factor of 1 and the losses are
1800 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 8kVA x 1 = 8kW
Output power = Input power - losses
Output power = (8kVA X 1) - 1800 = 8000 - 1800 = 6.2kW
Efficiency = (Output/input) x 100%, n = (6200/8000) x 100 = 77.5%
8) A transformer has a rated power of 1kVA and a power factor of 0.75 and the losses are
100 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 1kVA x 0.75 = 0.75kW
Output power = Input power - losses
Output power = (1kVA X 0.75) - 100 = 750 - 100 = 0.65kW
Efficiency = (Output/input) x 100%, n = (650/750) x 100 = 86.6%
9) A transformer has a rated power of 24kVA and a power factor of 0.95 and the losses are
1400 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 24kVA x 0.95 = 22.8kW
Output power = Input power - losses
Output power = (24kVA X 0.95) - 1400 = 22800 - 1400 = 21.4kW
Efficiency = (Output/input) x 100%, n = (21400/22800) x 100 = 93.9%
10) A transformer has a rated power of 12kVA and a power factor of 0.85 and the losses
are 600 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 12kVA x 0.85 = 10.2kW

Level 2 & Level 3 Electro-Technical Question Paper with Answers :

Level 2
1) A transformer has an input power of 20kW and power losses of 920W, the overall
efficiency is
a) 96%
b) 94%
c) 95%
d) 90%

2) What is this component? ( Gate / Anode / Cathode )
a) A transistor
b) A triac
c) A diac
d) A thyristor

3) What are the three main sections of a health and safety policy
a) Statement of intent
b) Organisation
c) Arrangements
d) The manual

4) Under the Management of Health and Safety at Work Regulations 1999, which of these
is an employee NOT entitled to do?
a) Use any equipment or substance after training
b) Report any serious or imminent danger
c) Operate unguarded machinery after training
d) Report employers health and safety shortcomings

5) It is the duty of all employees to:
a) Organise safety lectures
b) Carry out safe working practices
c) Provide suitable safety equipment
d) Repair damaged equipment

6) The sequence of control for a large installation can be MOST simply shown by
a) Wiring diagram
b) Layout diagram
c) Circuit diagram
d) Block diagram

7) A layout drawing shows a proposed cable run. The scale is 1:100 and the length on the
drawing is 65mm, the length of the cable is:
a) 6.5m
b) 17m
c) 42.5m
d) 4.25mm

8) What is meant by the term ‘zone of protection’?
a) Area around a working person
b) Zone around a bath
c) Zone around a lightning conductor
d) The area covered by an earthing system

9) If a ring main circuit has a 32 A fuse 230 V supply the maximum power available at any
one time is
a) 73.36 W
b) 736 W
c) 7360 W
d) 73600 W

10) BS 7671 does not apply to which of the following: (tick all that apply)
a) Aircraft
b) Motor vehicles
c) Mines
d) Outdoor lighting
Level 3

11) Two parallel plates of dimension 30mm by 20mm are oppositely charged to a value of
50mC. Calculate the electric flux density of the electric field.
a) 0.12C/m2
b) 83.3C/m2
c) 0.003C/m2
d) 3000C/m2

12) A 3-phase 4 pole, 50Hz induction motor has a slip of 4%. Rotor speed is:
a) 1500prm
b) 1440rpm
c) 1400rpm
d) 1359rpm

13) Which of these is a definition of ‘reasonably practicable’ in risk reduction
a) Minimum Cost And Effort
b) Major Cost But Minimal Effort
c) A Balance Of Effort And Costs
d) Major Cost With Major Risk Reduction

14) Which two of these are NOT true statements about ACOPs
a) They have a special legal status
b) Failure to observe an ACOP is not a criminal offence
c) Provide guides on practices other than health and safety
d) Can be approved without consent of the Secretary of State

Answers :

1) C Efficiency = Output/Input = (20000-920)/20000 x 100 = 95.4%.
I saw a similar question to this, with GOLA stating 20kVA.
2) D Thyristor. These have anodes and cathodes like diodes, but also have a gate.
3) A, B and C. Yes, they have manuals, but policy does not state it has to be in a manual! It
could be held on-line or in electronic format!
4) C Only manufacturer’s agents or trained authorised personal should remove guards
5) B
6) D
7) A In real life, the cable will be 100 times bigger than the dimension on the drawing.
65mm in m is 0.065. 100 x 0.065 = 6. 5m
8) C This term denotes the space within which a lightning conductor provides protection
against a direct lightning strike by diverting the strike to itself.
9) C P = V x I = 230 x 32 = 7360W
10) A, B and C
11) B Q = 50 x 10-3, A = 30 x 20 x 10-6 m2 OR 0.03 x 0.02 m2
D = Q
A
D = 50 x 10-3 = 83.3 C/m2
600 x 10-6
I have also seen this question with the word FLUX replacing FIELD, although field
is the correct term, as conceptualised by Michael Faraday.
12) B Ns = 1500 rpm. With 4% loss = 1440rpm
13) C
14) C, D
15) C
16) C
17) A They both have the same magnetisation strength. The area under the curve
represents the losses, so the wider the curve, the more magnetisation losses there
are.
18) C Similar to the cage rotor, except the bars are replaced by windings.
A and C. DOL is only used for starting.
19) C A and B would be examples of inappropriate PPE. The HSE don’t prevent accidents
directly, they provide guidance and enforcement.
20) D

 

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Electrotechnical Unit 302 :

A) A prospective earth fault current test needs to be carried out on a domestic
consumer unit which has type B circuit breakers. Some of the lighting circuits have fluorescent fittings.

1. State which instrument(s) can be used.
2. What precautions need to be taken prior to the test.
3. The minimum allowable value(s).
4. Describe the test.
(6 points)
B. Explain the terms
1. Equipotential bonding
2. Exposed conductive part

C. Draw a star-delta transformer arrangement.
1. Fully label all conductors, voltages and currents for a 25kV/400kV step-up system.

2. State two materials used for conductors in the UK generation, transmission and distribution system and why they are chosen.

Note: electro-technical level 2 and level 3 papers,
you will find quite a few questions which relate to this unit. Here are some examples
of what you may be asked (what is covered in the unit and should be known as underpinning knowledge):

_ Statutory safety regulations and safe working practices.
_ Selection of wiring systems and cable sizes
_ Be able to represent an installation using block, schematic, wiring or layout diagrams
_ Describe the generation, transmission, transformation, distribution and delivery of electricity in the UK
_ Describe single-phase and 3-phase supply types, voltages, currents and terminology

A) A prospective earth fault current test needs to be carried out on a domestic
consumer unit which has type B circuit breakers. Some of the lighting circuits have fluorescent fittings.

1. State which instrument(s) can be used.
2. What precautions need to be taken prior to the test.
3. The minimum allowable value(s).
4. Describe the test.

Answers
A) A prospective earth fault current test needs to be carried out on a domestic
consumer unit which has type B circuit breakers. Some of the lighting circuits have fluorescent fittings.

1. State which instrument(s) can be used.
2. What precautions need to be taken prior to the test.
3. The minimum allowable value(s).
4. Describe the test.

Answer:
1. PFC tester or loop tester with PFC function (as shown). The voltage range the meter will work on is from 50V to 480V, which is taken from the supply it is plugged into. It measures the current between line and neutral across an internal impedance inside the tester: PFC =
I = V/R = 230/0.5 = 460A. The meter will return a value from 0A up to ≈50kA.
The value can also be ascertained by calculation or determined by other means. ( 16th edition 713-12-01, ↔ 17th edition 612.11 )

2. This is a live test, you may be measuring live energised conductors (when using clip-on leads) so be very careful. As this is not the first live test, you will have already informed persons, put up warning signs, informed persons who could be affected by a ‘live’ test etc, but your tutor needs you to say this.
The other precautions required for a PFC test are for the person who is conducting the test to:
i) Check the condition of the test instrument and probes/leads for soundness
ii) Check test leads and probes conform to HSE GS 38
iii) Since you are working with live terminals, be careful not to touch any live part
3. To 16th edition:
Semi-enclosed (re-wire able BS 3036) SA1 = 1kA etc SA2 SA4
Cartridge fuses BS:1361 Type 1 = 16.5 kA Type 2 = 33kA

BS:88-2.1 = 50kA at 400V
BS:88-6 = 16.5kA at 230v & 80kA at 400v
BS EN 60898 MCBs (or old type MCB’s BS:3871)
M1 = 1kA / M1.5 = 1.5 kA / M2 = 2kA and so on
So, check your reading against the time current graphs for the relevant device to get an actual disconnection time.
.g. a 32A BS EN 60898 type B (BS3871 type 2) MCB has a reading of 460A, giving a
disconnection time from Appendix 3, fig.3.4 of 01.s to 5s (>160A), which is acceptable.

4. Measure the Prospective Fault Current at the origin of the supply.
Check that the test instrument, leads, probes and crocodile clips (if any) are suitable for the
purpose, and in good serviceable condition (to GS38).
Observing all precautions for safety, connect the instrument to the incoming energised
supply to measure a phase to neutral value.
Check the polarity indicator (if any) on the instrument for correct connection.
Using the PFC / Loop tester set the selector switch to PFC and the range switch to the
highest setting i.e. 2000A and test for the PFC value.
Reduce the range switch to a lower setting to obtain a more accurate value.
Measure the PSCC (Line (Phase) to Neutral) & PEFC (Line (Phase) to earth), measure at
the most remote socket and record the highest value as the PFC. Note: for 17th edition the
term ‘line’ must be used, for 16th edition, ‘phase’ is used.
Record this value in the Supply characteristics page and the Schedule of test results.
Ensure the breaking capacity of the main protective device is
capable of breaking the PFC (434-03-01 – 16th edition, 434.5.1 – 17th edition)
For 3-phase installations the PFC recorded is twice (2x) the maximum single-phase value measured.
instrument does not have a prospective fault current range, the readings given by the above
procedure are fault loop impedances (in ohms). Use a BS EN 61557-2 or BS EN 61557-3
compliant meter, which will deliver 20 to 25A for up to two cycles. To convert each of these
readings into a prospective fault current, divide them into the measured value of phase to
neutral voltage.
For example, if the voltage measured at the time of the test is 230V and the measured value
of fault loop impedance between phase and neutral at the origin is 0.05_.
Maximum prospective short-circuit = 230 / 0.05 = 4600 A (or 4.6 kA) current (line (phase) to neutral).
If Ze is known and the loop tester does not have the facility to measure earth fault current,
it can also be calculated by using the formula below:
Ipf = Uo / Ze Where Ipf = Earth Fault Current, Uo = Nominal Phase to Earth Voltage, Ze = External Earth Fault Loop Impedance

A.) If the test
LCD, display : Main status indication LED : Range switch : Test Button : PS, always remember Polarity :

B. Explain the terms

1. Equipotential bonding :
2. Exposed conductive part :

B. Explain the terms

1. Equipotential bonding
2. Exposed conductive part
1.Equipotential bonding: 16th / 17th edition: ‘Electrical connection maintaining various
exposed-conductive-parts and extraneous-conductive-parts at substantially the same potential.’

This involves joining together metalwork that is or may be earthed so that it is at the same
potential to prevent shock from between those pieces of metal as the earth system handles a fault.

2. Exposed conductive part: ** 16th edition: A conductive part of equipment which can be
touched and which is not a live part but which may become live under fault conditions.’
** 17th edition: ‘Conductive part of equipment which can be touched and which is not
normally live, but which can become live when basic insulation fails.’
This refers to items like the metallic covers of electrical equipment which will normally be
at earth potential, but which may develop a voltage if the fault current goes through the equipment.

C. Draw a star-delta transformer arrangement
1. Fully label all conductors, voltages and currents for a 25kV/400kV step-up system.

2. State two materials used for conductors in the UK generation, transmission and distribution system and why they are chosen.
Aluminium is used for high voltage conductors on overhead pylons on the Supergrid, National grid and to large industry. Aluminium has a slightly higher resistivity than copper ,←← but is much lighter, the main reason it is chosen for overhead lines. The aluminium
conductors are on the outside woven like a rope around a steel core, which provides mechanical strength.
Copper is used for underground cabling in the transmission and distribution systems or where weight is not an issue. It is also used for medium industry right down to domestic supply due to its low resistivity. Although Gold has lower resistivity, it is not used due to its high cost.

C. Draw a star-delta transformer arrangement.
1. Fully label all conductors, voltages and currents for a 25kV/400kV step-up system.

2. State two materials used for conductors in the UK generation, transmission and distribution system and why they are chosen.

examples of what you may be asked (what is covered in the unit and should be known as underpinning knowledge):
_ Statutory safety regulations and safe working practices.
_ Selection of wiring systems and cable sizes
_ Be able to represent an installation using block, schematic, wiring or layout diagrams
_ Describe the generation, transmission, transformation, distribution and delivery of electricity in the UK
_ Describe single-phase and 3-phase supply types, voltages, currents and terminology

 

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Protective Conductors :

Where the protective conductor is formed by conduit , ( 543.2.7 ) trunking , ducting or the metal sheath and/or armour of a cable ,
The earthing terminal of each accessory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure ,

Except where the circuit protective conductor is formed ( 543.2.9 ) by a metal covering or enclosure containing all of the conductors
Of the ring , the circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends
Connected to the earthing terminal at the origin of the circuit ,

A switching device shall Not be inserted in a protective ( 543.3.4 ) conductor unless :
* the switch has been inserted in the connection between the Neutral point and means of earthing ; and
* the switch is linked switch arranged to disconnect and connect the earthing conductor for the appropriate source , at substantially the same time the related live conductors ,

Where electrical monitoring of earthing is used , no ( 543.3.5 ) dedicated devices ( e.g. operating sensors , coils ) shall be connected
In series with the protective conductor , ( see BS-4444 )

Earth Electrode Résistance :

Where the Earthing system incorporates an Earth Electrode ( 612.7 )
As part of the installation , the Electrode Résistance to Earth shall be measured ,

Where the installation incorporates an Earth Electrode , the ( 612.1 ) test of Regulation ( 612.7 ) shall also be carried out before the Installation is energised ,

If any test indicates a failure to comply , that test and any preceding test , ( 612.1 ) the results of which may have been influenced by fault indicated , shall be repeated after the fault has been rectified ,

Where Fluorescent or Discharge lighting is involved , a factor of 1.8 is used to take into consideration control gear :
Fluorescent fitting will have a current rating off ?
80W x 1.8 ÷ 230 = 0.63A

Light levels :

Light levels available where the camera is to be used are an important consideration. shows some typical light levels.
When choosing a suitable camera for a particular environment, it is best to select one that is specified at approximately ten times the minimum light level for the environment. One that is specified at the same level of light will not produce the clear
images needed, because the camera will not have enough light to ‘see’.

Environment : Typical light level
Summer sunlight : 50,000 lux
Dull daylight : 10,000 lux
Shop/office : 500 lux
Main street lighting : 30 lux
Dawn/dusk : 1–10 lux
Side street lighting : 3 lux
Typical light levels

 

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Are you installing smoke alarms ? Are you confused when it comes to the 17th Edition ? Too many conflicting views ? We have put together a little smoke and fire alarms guide to the 17th edition.
Smoke alarms can be connected to a lighting circuit – this is the preferred circuit
The alternative is wiring on a dedicated circuit

Who says this?
Most reputable smoke alarm manufacturers.
The IEE , NICEIC , ECA , and SELECT

The 17th Edition : does not make any reference to domestic smoke alarm installations in the whole document.
Why are some manufacturers saying that smoke alarms should be wired on a dedicated circuit ?
They are misinterpreting the requirements of Chapter 56 – Safety Services. This makes reference to fire detection and alarm systems, but in section 560.10 it refers you to BS 5839 for the specific requirements. Appendix A makes it quite clear that BS 5839 : Pt 1 , is the document being referred to. This standard is for commercial systems , it is not the standard for domestic smoke alarms systems, this is BS- 5839 : Pt 6 ,
In the absence of specific advice in the 17th Edition for domestic smoke alarm systems
to Grade D (mains with a back-up battery), follow the recommendations of BS-5839 : Pt 6 ,

What are these recommendations exactly?

Clause 15.5 states that Grade D smoke alarms can be wired from either…
* ‘An independent circuit at the dwellings main distribution board, in which case no other electrical equipment should be connected to this circuit’.
* Or ‘A separately electrically protected, regularly used lighting circuit’.
* Note that RCD protection is not mentioned. Therefore, an RCD protected circuit is acceptable.
* Hard-wired systems must be on a single final circuit.
* Radio – linked systems must be on a single final circuit.
* Radio – linked systems can be on separate lighting circuits.

- Temporary Electrical Installations for Structures ,
Amusement devices and booths at fairgrounds , Amusement parks and circuses ,

The protective measures of no-conducting location and earth-free local equipotential bonding are Not permitted , ( 740.410.3.6 )
Where the type of system earthing is TN-: ( 740.411.4 )

* a PEN conductor shall not be used downstream of the origin of the temporary electrical installation ,
* the final circuits for the supply to caravans or similar shall not include a PEN conductor ,

Where a generator supplies a temporary installation , ( 740.551.8 )
Forming part of a TN, TT , or IT system , care shall be taken to ensure that the earthing arrangements are in accordance with the regulations ,

- The following types of protective device may be used for fault protection in a TN system , ( 411.4.4.)

* an Overcurrent protection device ,
* an RCD ( in which case the circuit should also incorporate overcurrent protective device ,

Note : Compliance with regulations 411.4 shall be verified by :
* measurement of earth fault loop impedance ;
* verification of the characteristics and / or the effectiveness of the associated protective device ,

Part 2: Definitions for the classification of persons

„ The 17th edition identifies three categories of people
„ * A skilled person who has technical knowledge to enable them to avoid electri
cal dangers
„* An instructed person who has been adequately advised or supervised to
avoid electrical dangers – e.g. facilities manager
„* An ordinary person – typically a member of the general public

FAIRGROUNDS , AMUSEMENT PARKS AND CIRCUSES

Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses – a proposed new Section for BS 7671:2008, 17th Edition of the IEE Wiring Regulations. Currently, there is no Part or Section of BS 7671:2001(2004) covering such installations but information can be found in IEC 60364-7-740 and HD 60364-7-740. The proposed Section 740 of BS
7671:2008 is based on the CENELEC Harmonised Document HD 60364-7-740, of which, the UK is to incorporate the technical intent of that standard. (Please note that Regulations and Sections quoted within this article are from the proposed BS-7671:2008 and may be subject to
The Scope of Section 740
Section 740 recognises that some installations are exposed to many differing and onerous circumstances, as they are frequently installed,
dismantled, moved to a new location then installed and operated again. To compound problems, such installations can be exposed to the
elements, open to the general public, house animals and livestock and be operated as a place of work. The equipment must function without
compromising safety, therefore, the installation has to be fit for purpose and be designed to cope with ever-changing conditions.
The permanent electrical installation, from which the temporary system is supplied, or the building in which the temporary system is
housed, is excluded from the scope, nor does the scope apply to the internal electrical wiring of machines (see BS EN 60204-1).

Electrical Supplies
The nominal supply voltage of temporary electrical installations in booths, stands and amusement devices should not exceed 230/400 V ac or
440 V dc. Supplies can be obtained from a number of sources:
* from the public network, i.e. the DNO ,
* generators, i.e. those mounted on trucks owned by the touring event ,
* from privately owned supplies, i.e. a local factory with sufficient spare capacity , There can be any number of electrical sources supplying the temporary system and it is of paramount importance that line-and neutral
conductors from different sources are not interconnected. Where the supply is obtained from the DNO any instructions given must be adhered to. Supplies obtained from the DNO would preferably be TN-S but this isn’t always possible. A TN-S system has the neutral of the source of energy connected with earth at one point only, at, or as near as is reasonably practicable, to the source of supply. The consumer’s main earthing terminal is typically connected to the metallic sheath of the distributor’s SWA service cable. Where the available supply is TN-C-S, the supply should not be used in that form, i.e. a TT system should be created. The reason is that the ESQCR prohibits the use of a TN-C-S system
for the supply of a caravan or similar construction. Where continuity of service is important, IT systems may be used for dc applications only.

Protection against electric shock
At the origin of each electrical supply, to all or part of the installation, an RCD, with a rated residual operating current not exceeding 300mA, is to be installed to provide automatic disconnection of supply. As there will be further RCDs downstream of this point, this RCD should be of the
S-type, complying with the requirements of BS EN 61008-1 or BS EN 61009-1 and incorporate a time delay in accordance with BS EN 60947-2, to provide discrimination with further RCDs protecting final circuits. For supplies to ac motors, RCDs. should be the time-delayed or the
S-type where necessary to prevent unwanted tripping. The protective measure of protection by obstacles is not permitted on this type of installation, however, placing out of arm’s reach is acceptable for electric dodgems ,

Additional protection
All final circuits in the installation, e.g. lighting, socket-outlets rated up to32 A, mobile equipment connected by a flexible cable and rated up to 32 A are to be protected by an RCD having a rated residual operating current not exceeding 30 mA. The requirement for additional protection relates to the increased risk of damage to cables within an installation of this nature.

Lighting circuits incorporating emergency luminaires, with self-contained batteries for example, should be protected by the same RCD
protecting that lighting circuit. This requirement for additional protection does not apply to:
* SELV or PELV circuits – this measure alone is deemed to be a protective measure in all situations ,
* circuits protected by electrical separation
* lighting circuits placed out of arm’s reach – provided they are not supplied by socket-outlets, i.e. those manufactured to BS 1363 or
BS EN 60309-1; luminaire supporting couplers or plug-in lighting distribution units excepted

Supplementary bonding
Particular care must be taken in areas where livestock are housed as they are sensitive to small potential differences. To minimise potentials,
supplementary bonding should be installed to connect all exposed conductive-parts and extraneous conductive-parts that can be touched by livestock. Where a metal grid is laid in the floor, or extraneous-conductive-parts are accessible, they should be included within the supplementary bonding of the location. It is important to note that animal excrement and urine is very corrosive and so all supplementary bonding connections should be enclosed in a suitable enclosure.

THE INSTALLATION
Wiring systems
Conduit, cable trunking and ducting, tray and ladder systems can be used but must, of course comply with the manufacturer's instructions; the
following standards apply:
* conduit systems BS EN 61386 series
* cable trunking systems/cable ducting systems BS EN 50085
(particular parts only)
* tray and ladder systems BS EN 61537

 

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Cables
All cables should be fire rated and meet the requirements of BS EN 60332-1-2. Cables of type H07RNF or H07BN4-F (BS 7919)
together with conduits complying with BS EN 61386-23 are deemed to satisfy this requirement. Cables should have a
minimum rated voltage of 450/750 V, except that, within amusement devices, cables and cords having a minimum rated voltage of 300/500 V
may be used. Where cables are buried in the ground, the route should be marked at suitable intervals and be protected against mechanical damage.

Electrical connections
Joints should not be made in cables except where necessary as a connection into a circuit. Where joints are made, these should be either using
connectors in accordance with the BS-7671, the manufacturer’s instructions or the connection should be made in an enclosure with a degree of
protection of at least IP4X or IPXXD. Where strain can be transmitted to terminals the connection should incorporate cable anchorage(s).

External influences
Electrical equipment should have a degree of protection of at least IP44.

Switchgear and controlgear
Switchgear and controlgear should be placed in cabinets which can be opened only by the use of a key or a tool, except for those parts designed
and intended to be operated by ordinary persons.

Isolation
It is a requirement that every electrical installation of a booth, stand or amusement device has its own means of isolation, switching and
overcurrent protection, these devices should be readily accessible. There are similar requirements for supplies to amusement devices. Additionally, each distribution circuit should be provided with its own readily accessible and properly identified means of isolation.
A device for isolation should disconnect all live conductors – line(s) and neutral conductors.

Examples of devices used for isolation are:
* circuit-breaker
*RCD
* plug and socket arrangement

Luminaires
Every luminaire and decorative lighting festoon-chain should have a suitable IP rating and be securely attached to the structure or support
intended to carry it. Its weight should not be carried by the supply cable, unless it has been selected and erected for this purpose.
Luminaires and decorative lighting festoon-chains mounted less than 2.5 m, i.e. arm’s reach, above floor level or could be otherwise accessible to incidental contact, should be firmly fixed, sited and guarded to prevent risk of injury to persons or ignition of materials. Access to the fixed light source should only be possible after removing a barrier or an enclosure, which should only be possible by the use of a tool. Lighting festoon-chains should use H05RN-F (BS 7919) cable or equivalent, they may be used in any length provided the overcurrent protective device in the circuit is correctly rated. Luminous tube, sign or lamps with an operating voltage higher than 230 V/400 V a.c., e.g. neon signs, are to
be installed out of arm’s reach or be adequately protected from accidental or deliberate damage. A separate circuit should be used which should be circuit should be used which should be controlled by an emergency switch. controlled by an emergency switch.
The switch should be easily visible, accessible and marked in accordance with the requirements of the local authority.
Luminaires in shooting galleries and other sideshows where projectiles are used should be suitably protected against accidental or deliberate damage. When transportable floodlights are used, they should be mounted so that the luminaire is inaccessible to no instructed
persons. Supply cables should be flexible and have adequate protection against mechanical damage.

Safety isolating transformers and electronic converters
Safety isolating transformers should comply with BS EN 61558-2-6 or provide an equivalent degree of safety. Each transformer or electronic
converter should incorporate a protective device which can be manually reset only; this device should protect the secondary circuit.
Safety isolating transformers should be mounted out of arm’s reach or be mounted in a location that provides equal protection, e.g. in a panel or
room that can only be accessed by a skilled or instructed person, and should have adequate ventilation. Access by competent persons for
testing or by a skilled person competent in such work for protective device maintenance should be provided. Electronic converters should
conform to BS EN 61347-2-2. Enclosures containing rectifiers and transformers should be adequately ventilated and the vents should not be
obstructed when in use.

Plugs and socket-outlets
An adequate number of socket-outlets should be installed to allow the user's requirements to be met safely. In booths, stands and for fixed
installations, one socket-outlet for each square metre or linear metre of wall is generally considered adequate. Socket outlets dedicated to lighting circuits placed out of arm’s reach should be labelled according to their purpose. When used outdoors, plugs, socket outlets and couplers should comply with BS EN 60309-2, or where interchange ability is not required, BS EN 60309-1.

FIRE RISK
Luminaires and floodlights
Luminaires and floodlights should are to be fixed so that a focusing or concentration of heat is not likely to cause ignition of any material.

Electric motors
An electric motor which is automatically or remotely controlled and which is not continually supervised should be fitted with a
manual reset protective device against excess temperature.

Electrical supply to devices
At each amusement device, there should be a connection point readily accessible and permanently marked to indicate the following essential
characteristics:
* rated voltage
* rated current
* rated frequency

Electric dodgems
Electric dodgems should only be operated at voltages not exceeding 50 V a.c. or 120 V d.c. The circuit should have an electrical separation
from the electrical supply by means of a safety isolating transformer in accordance with BS EN 61558-2-4 or a motor-generator set.

Low voltage generating sets
It is very important that all generators are located to prevent danger and injury to people through inadvertent contact with hot surfaces and
dangerous parts. The electrical equipment associated with the generator should be mounted securely and, if necessary, on anti-vibration mountings. Where a generator supplies a temporary installation, forming part of a TN, TT or IT system, care should be taken to ensure that the earthing arrangements are adequate and, in cases where earth electrodes are used, they are considered to be continuously effective. In reality this means that the drying of the ground, in summer, or freezing of the ground, in winter, should not adversely affect the value of earth fault loop impedance for the installation. The neutral conductor of the starpoint of the generator should, except for IT systems, be connected to the
exposed-conductive-parts of the generator.

INSPECTION AND TESTING The temporary installation
The electrical installation between its origin and any electrical equipment should be inspected and tested after each assembly on site. Internal
electrical wiring of roller coasters, electric dodgems, etc., are not considered as part of the verification of the electrical installation. In special
cases the number of the tests may be modified according to the type of temporary electrical installation. The HSE offers guidance on the
inspection and testing of the temporary electrical installation in the publication HSG 175 – Fairgrounds and Amusement Parks: Guidance on Safe Practice.

BS 1363 – 13 A plugs, socket-outlets and adaptors
BS 7919 – Electric cables. Flexible cables rated up to 450/750V, for use with appliances and equipment intended for industrial and similar environments
BS EN 50085 – Cable trunking and cable ducting systems for electrical installations
BS EN 60204-1 – Safety of machinery. Electrical equipment of machines. Specification for general requirements
BS EN 60309-1 – Plugs, socket-outlets and couplers for industrial purposes. General requirements
BS EN 60309-2 - Plugs, socket-outlets and couplers for industrial purposes. Dimensional interchange ability requirements for pin and contact-tube accessories
BS EN 60332-1-2 – Tests on electric and optical fibre cables under fire conditions. Test for vertical flame propagation for a single insulated wire or cable. Procedure for 1 kW pre-mixed flame
BS EN 60947-2 – Low-voltage switchgear and control gear. Circuit-breakers
BS EN 61008-1 – Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCBs).
General rules
BS EN 61009-1 – Residual current operated circuit breakers with integral overcurrent protection for household and similar uses (RCBOs). General rules
BS EN 61347-2-2 – Lamp controlgear. Particular requirements for d.c or a.c. supplied electronic step-down convertors for filament lamps
BS EN 61386 – Conduit systems for cable management. General requirements
BS EN 61537 – Cable management. Cable tray systems and cable ladder systems
BS EN 61558-2-6 – Safety of power transformers, power supply units and similar. Particular requirements for safety isolating transformers for general use
IEC/HD 60364-7-740 – Electrical installations of buildings – Part 7-740: Requirements for special installations or locations – Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses
HSG 175 – Fairgrounds and Amusement Parks: Guidance on Safe Practice ISBN 978-0-7176-6249-4

 

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Low power supply sources : ( 560.6.10 ) limited to 500W for 3-hour duration or 1500W for 1-hour duration
However ,
* the batteries may be of the gastight or valve regulated maintenance – free type ; and
* the minimum design life of the batteries shall be 5 years ,

Multiphase circuits , it shall be verified that the Phase sequence is maintained , ( 612.12 )

Connections :

Every connection shall be accessible for inspection , ( 526.3 ) testing and maintenance , except for the following :
* a joint designed to be buried in the ground ,
* a compound filled or encapsulated joint ,
* a connection between a cold tail and the heating , element as in ceiling heating , floor heating or a trace heating system ,
* a joint by welding , soldering , brazing or appropriate compression tool
* a joint forming part of the equipment complying with the appropriate product standard

Wiring systems : ( 132.7 )
The choice of the wiring system and the method of installation shall include consideration of the following ,
* the nature of the location ,
* the nature of the structure supporting the wiring ,
* accessibility of wiring to persons and livestock ,
* voltage ,
* the electromechanical stresses likely to occur due to short-circuit and earth fault currents ,
* electromagnetic interference ,

Safety of machinery - Electrical equipment of machines - Part 1: General requirements

Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses

IEC 60204-1:2005+A1:2008 is applicable to the electrical equipment or parts of the electrical equipment that commences at the point of connection of the supply to the electrical equipment of the machine and operate with nominal supply voltages not exceeding 1 000 V for alternating current (a.c.) and not exceeding 1 500 V for direct current (d.c.), and with nominal supply frequencies not exceeding 200 Hz. The technical content is therefore identical to the base edition and its amendment and has been prepared for user convenience. A vertical line in the margin shows where the base publication has been modified by amendment 1. This consolidated version consists of the fifth edition (2008) and its amendment 1 (2008). Therefore, no need to order amendment in addition to this publication.

Safety Circuits :
In addition to a general schematic diagram, full details of all electrical safety sources shall be given. The information shall be maintained and displayed adjacent to the relevant distribution board. A single-line diagram is sufficient. ( 560.7.9 )

Bonding on sink ?

Probably not.
On-Site Guide section 4 states that:
Supplementary bonding is required by BS-7671 / 701.415. in some locations.
(Generally in Special Locations. A kitchen or utility room is not one of these).
However, if the installation meets the requirements for earthing and bonding (i.e. Main earth connection and Main bonding of gas and water, metal waste pipes etc. 411.3.1.2 ) then there is no specific requirement for supplementary bonding of:
• Kitchen sinks, pipes or draining boards
• Metallic boiler pipework
• Metal furniture in kitchens
• Locations containing bath or shower providing the requirements of BS-7671:2008 701.415. are met. ( Disconnection time of 0.2 for, TT 0.4 for TN and RCD protection).

How close to a sink/basin can sockets be located ?

BS7671:2008 does not specify any minimum distance for socket outlets to be sited from a sink.
Regulation 512.2.1 requires external influences to be considered when selecting equipment for a particular location.

The regulation requires all equipment to be of a design appropriate for the situation in which it is to be used. Sockets that are used in domestic installations are not splash resistant, are therefore not suitable for installation close to any sink or draining board.
It is recommended that socket outlets and other accessories should be located at least 300mm, measured horizontally from a sink or draining board, where they are unlikely to be splashed.

Does the dispensation in Regulation 701.415.2 to omit supplementary bonding in a bathroom apply to TT systems ?

Yes it does apply to TT systems.
Regulation 701.415.2 states that supplementary bonding may be omitted where:
• i) All final circuits in that location comply with 0.4 sec disconnection
• ii) All final circuits in that location are protected by RCD
• iii) Main bonding to extraneous conductive parts is intact.
In this case TT systems are treated in the same way as TNC-S & TNS.

Is a time-delayed RCD main switch required in the consumer unit of a new domestic installation supplied by a TT system ?

Provided that the consumer unit is of all insulated construction and all the final circuits are RCD-protected, a time-delayed RCD main switch is not required.

I am measuring a Zs of 140Ω on my final circuits. Table 41.3 gives a maximum of 1.44Ω. I know that a Ze below 200Ω on a TT system is acceptable (Table 41.5 note 2). Is my Zs ok ?

Yes it is acceptable. As long as your circuit is protected by an RCD. In this case (at the front end) they should be RCBOs to give double pole isolation. The maximum Zs which ensures the operation of a 30mA RCD (circuits not exceeding 32A) is 1,667Ω . (Table 41.5) . Regarding your Ze measurement. A Ze greater than 200Ω is considered unstable and it may be prudent to install further electrodes.

TT circuits require a disconnection time of 0.2 seconds. (BS7671 Table 41.1).
How can this be achieved when the Max Loop Imp Tables in BS7671 only deal with 0.4 and 5 seconds ?
BS-7671:2008 ,
The note below Table 41.1 states that:

TT disconnection time of 0.2 secs up to 32A & 1 sec over 32A (411.3.2.4) is achieved by:
1. an Overcurrent Protective Device and
2. Equipotential Bonding (connected to all extraneous metallic parts).

Then the disconnection times for TN systems can be used ie. 0.4 seconds up to 32A & 5 secs over 32A (411.3.2.3)
On – site Guide Section 3 Disconnection Times for TT circuits. The required disconnection times for TT systems can (except in the most exceptional circumstances) only be achieved by protecting every circuit with an RCD.

BS-7671:2008 / 411.3.2.2 On – site Guide Section 3

 

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Should I identify black or grey as neutral on harmonised single phase cables ?
Technically, when any cable is over-sleeved or marked (with the exception of single-core green/yellow which must not be over-sleeved or marked), the over-sleeve or marking takes precedence over any colour underneath and therefore any combination can be used.

However, a convention has been generally accepted of over sleeving or marking the black with green/yellow (CPC) and the grey with blue (Neutral).

The thinking behind this has been done with the aim of helping disassociate the colour black with neutral and the shade of grey being a neutral colour.

How Long Can Meter Tails Be ?
The length of Tails from the Meter to the Consumers Distribution Board or Consumer Unit is at the discretion the Local Electricity Company.

Generally the maximum length of tails allowed is 3 metres. For longer distances it is common practice to install a Double Pole Isolation Switch at the Meter Position and install tails or a Sub-Main to the Consumers Distribution Board. Care should be taken to install adequate mechanical protection to the Tails or Sub-Main cable.

SWA is preferable if the cable is not to be clipped direct to surface. Minimum size of Meter Tails is 25 sq mm Onsite Guide Section 2

Building Regulations confirm...

...that when a hole is cut into a fire rated ceiling to fit a downlight, the fire stopping ability of the ceiling is impaired. In the event of a fire, flames could penetrate through the light fitting and spread to the floor above with the subsequent risk to life and property. The downlight itself can also be a source of fire due to the high temperature of lamps and the promixity to flammable material.

To provide total peace of mind and total protection, a Fire hood downlight cover should be installed over the light fitting if the ceiling is a fire separating element. Fire hoods will stop the spread of fire for at least 60 minutes. In fact, recent tests by Chiltern International have demonstrated that Fire hood downlight covers can give added peace of mind by providing up to 2 hours protection from fire.

When Fire hood / downlight covers are fitted as part of the ceiling structure they become in effect a permanent fixture. This means that the fire protection with Fire hood remains even when fashion may dictate a change of light fittings.

“Building Regulations 2000 Approved Document P allocates full responsibility to the electrician to make good the fire performance of any fire-rated floor/ceiling/wall after carrying out an electrical installation and legal action can be taken for non-compliance. Many, so called fire rated downlight fittings/covers are only tested in a small number of ceiling constructions and consequently this leaves the electrician vulnerable to “legal action” if the solution that he uses is wrong for the installation."

Types of Smoke Alarm Sensor : The following smoke alarm sensor types are suitable for different applications.

Optical :
Sensitive to larger smoke particles produced by smouldering fires like furniture. Suitable for mounting in landings and hallways to reduce false alarms from kitchens but not in steamy areas near to showers or bathrooms.
Ionisation :
Sensitive to smaller invisible particles in smoke which can be produced from cooking. Suitable for dusty or occasionally Smokey locations as they are less sensitive to more dense smoke particles. More likely to cause false alarms than the Optical when near kitchens.

Heat:
Not sensitive to any smoke.

Suitable for kitchens but only when linked to smoke detectors which are mounted in circulation areas such as hallways and landings.

Sitting :
Must be at least 300mm from a wall, corner or light fitting.
On sloping ceilings sensors must be 900mm (horizontally) from apex.At least one on each floor area (hall & landing).One sensor between lounge or kitchen and bedrooms.

Linking :
A mains voltage system requires linking between sensors with 3 core & earth cabling, however radio frequency or Radio Link bases can be used to prevent the need for wiring.

Sounders :
Each mains or battery operated sensor must incorporate an integral sounder.

Part P of the building Regulations deals with Fire Safety in dwellings.

For the Deaf & Hearing Impaired : Smoke & Heat Alarms
People with hearing difficulties require a different approach to fire protection, a conventional alarm sounder will not be sufficient for their needs.

System Features & Benefits :
• Control panel with rechargeable battery back-up, mains power supply lead and 13 amp Plug
• High intensity integral strobe light
• Auxiliary socket for connection of additional optional strobe lights
• Vibrating pad for placing under a pillow or mattress
• Capability for interconnection of up to 12 smoke alarms
• Test button on control panel for testing the system
• Connections are monitored to check integrity of system
• Alarm clock input facility
• Remote trigger option
• Pager output facility

 

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Inefficient Incandescent (GLS) Lamps to go ←←
Over an eight year period the ‘old type GLS’ land inefficient lamps will disappear from the shelves of suppliers and their sale will be prohibited within the EU. The EU directive begins in September 2009 with lamps of 80 Watts or higher, as well as all frosted (non-energy saving) lamps.

By 2012, most lamps of greater than 7 watts will be withdrawn from sale. Special purpose incandescent lamps (e.g. those used in household appliances such as ovens or fridges, traffic lights, infrared lamps etc.) are meant to be exempt from the measure, as they cannot fulfil the efficiency requirements and most of the time there is no alternative lamp technology.

The table below shows when certain requirements will be enforced and also displays some examples of the types of lamps, commonly used in households that will be affected by the new requirements.

* 1 Sept 2009 Lamps rated at 100w or more must carry an energy rating of C or better. All others may carry E : Lamp types prohibited from retail (common in households) [1] Clear incandescent and conventional halogen lamps rated at 100w or more [2] All frosted lamps excluding those carrying an energy rating of A (CFLs) * 1 Sept 2010 Lamps rated at 75w or more must carry an energy rating of C or better. Lamp types prohibited from retail (common in households) Clear incandescent and conventional halogen lamps rated at 75W or more : * 1 Sept 2011 Lamps rated at 60w or more must carry an energy rating of C or better. Lamp types prohibited from retail (common in households) Clear incandescent and conventional halogen lamps rated at 60w or more * 1 Sept 2012 Lamps must carry an energy rating of C or better All clear incandescent and conventional halogens : Lamp types prohibited from retail (common in households) ( Halogen lamps rated B & C still ok ) * 1 Sept 2013 Raising of quality requirements followed by a review * 1 Sept 2016 Lamps must carry an energy rating of B or better with 1 exception : Lamp types prohibited from retail (common in households) All lamps carrying an energy rating of C except special cap halogens (C rating

Spotlamps and other directed or reflected lamps will not be regulated until a second directive is drawn up at the end of 2009.

Halogen lamps with special caps like G9 do not exist with energy classes better than C. They are needed on the market as there are luminaires that can only take such lamps. Therefore further improvements can only be achieved by imposing requirements on the luminaires themselves, which the Commission is planning to do in a measure currently under preparation and to be tabled in 2009.

Halogen dichroic spots & floods which are widely used in surface mounted and recessed lighting applications, have a higher light output for power used and therefore lamps with an energy rating of C or better will not be phased out.

 

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to view the effects of installing a floodlight at various angles :

domestic locations is a 250 or 500 watt tungsten halogen floodlight controlled by a movement sensor (passive infra-red, PIR).

90o - At an angle of 90 o degrees from the vertical, the light is shining directly outwards, making it impossible for onlookers to see any criminal activity.

At 67o, the problems persist as at 90o degrees, making your "security" light a serious security risk.

45 o - The floodlight has an opening angle of 72o degrees, and so the light needs to be angled at less than half that (i.e. less than 36o) to illuminate the background (in this case, a wall).

At 22o, the floodlight begins to become a security aid. The house wall is illuminated, and so any intruder is highlighted against the background even if (as in this case) the background (i.e. the gate) is dark. However, when standing close by, the light source is still visible, which impedes the ability of a nearby witness to identify an intruder.

O o - Pointing a floodlight directly downwards is the best solution. The background wall is illuminated, and the bulb of the floodlight is no longer visible, making it easier on the eye. However, the floodlight is still over-powered (in this case, a 500W bulb); such a bulb will always generate strong shadows for people to hide in. The best overall solution is a floodlight pointing directly downwards whilst using a low powered bulb (60-120W will aid onlookers, without generating glare).

 

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Wiring within the trunking should be to a maximum of 45% of the available capacity in line with IEE wiring regulations.

* It is important to maintain electrical continuity between the cover and the base for the integrity of the system, and adherence to standards.

 

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The customer

Following initial verification, BS 7671 requires that an Electrical Installation Certificate, together with a schedule of test results and an inspection schedule, should be given to the person ordering the work. Until this has been done, the Regulations have not been met.
Sometimes the person ordering the work is not the end-user, e.g. the builder of a new housing estate sells the individual houses to various occupiers. In these cases it is recommended that copies of the inspection and test certificates, together with a test results schedule, are passed on to the new owners.

Handover to customer

Handover of the installation to the customer is the final task. This should include a tour of the installation, an explanation of any specific controls or settings and, where necessary, a demonstration of any particularly complicated control systems. The operation and maintenance manuals produced for the project should be formally handed to the customer at this stage, including copies of the Electrical Installation Certificate, the Schedule of Test Results and the Inspection Schedule

Activity
1. Obtain copies of the Electrical Installation Certificates, Inspection Schedules and Schedules of Test Results for your home or the site that you are currently working on. If the building is old enough these will also be accompanied by one or more Periodic Inspection Reports. If you can, compare these with the current installation to see if any alterations or additions have been made since they were prepared.

2. Have a look at any test equipment you have access to and see when and how it was last calibrated and when it is next due for calibration.

3. If you have not done any ‘real’ inspection and testing before, you might like to’ work shadow’ someone while they are carrying out an inspection and testing of an installation

Functional testing of residual current devices (RCDs)

Where a residual current device (RCD) fails to trip when pressing the integral test button, this would indicate a mechanical fault within the device itself, which should therefore be replaced.

When a residual current device fails to trip when being tested by an RCD tester, this would suggest that there is a fault with the RCD and that it should be replaced. It maybe that there is an issue with the cpc; however a test of the earth-loop impedance would prove whether this is satisfactory or not.

If the RCD does trip out, but not within the time specified, then a check should be made that the test instrument is set correctly for the nominal tripping current of the device under test. If the correct tripping current was selected then this indicates that the would fail to give the protection required and, therefore, would need replacing.

A RCD is fitted to the circuit for safety and protection. If the device is not working, then the installation is not protected and people and livestock are at risk of electric shock

Initial verification procedures

In order to make sure that this work is carried out satisfactorily the inspection and test procedure must be carefully planned and carried out and the results correctly documented .
We inspect and commission material after the completion of work for three key reasons to ensure:

* compliance with BS 7671
* compliance with the project specification (commissioning )
* that it is safe to use.

 

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Portable Appliance Testing - PATS

Examples of Bad Practice

No matter how well maintained you believe your electrical system to be there can be faults or unsafe areas that need correcting. Below are some of the more common problem areas.

Common Office Hazards

Incorrect Fuse Rating

Incorrect Polarity

Un-earthed appliances

Splits in cables

Trapped cables, between objects. (example: between desks and walls)

Trapped Cables (example; in floor boxes)

Overloading of sockets by 'piggy-backing' extension leads

Incorrect use of extension cables

Use of double adapters

Unsheathed pins on plugs

Un-earthed metal frame desks

Trailing leads

Water vessels near to electrical points

No access to sockets to disconnect in an emergency

Equipment such as fan heaters getting clogged and overheating

Dust clogging electrical equipment

Extension Leads

Extension leads are also considered as portable equipment and should be avoided where possible. If used, they should be tested as portable appliances. It is recommended that 3-core leads (including a protective earthing conductor) be used.

A standard 13 A 3-pin extension socket-outlet with a 2-core cable should never be used even if the appliance to be used is Class II, as it would not provide protection against electric shock if used at any time with an item of Class I equipment.

** Class I equipment is earthed and contains metal parts, e.g. storage heaters, washing machines
** Class II equipment is not earthed and is usually in a plastic case, e.g. hairdryers, fans

Guidance for Schools & Colleges

Headteachers and others responsible for the safety of pupils and staff need to ensure that electrical equipment is regularly maintained and electrical hazards are identified and dealt with promptly.

The Health and Safety at Work Act and The Electricity at Work Regulations cover the legal requirements for electrical safety and apply to all places for work, including educational establishments.

Under the Regulations, every employer has a duty to ensure that all reasonable precautions are taken to achieve electrical safety. In the case of schools and colleges, the headteacher will normally be regarded as the principal 'duty holder'. The principal duty holder is required to:

• ensure that installation, repair and maintenance work is only carried out by competent persons
• confirm the safety of equipment by arranging periodic inspection and testing and any necessary maintenance work
• implement and maintain safety procedures for all electrical equipment in use.

 

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If adhesive tape is used , then it has been bicoloured : ( PEN )

* PEN ; conductors’ ( when insulated ) are either
Green & yellow : throughout their length . with blue markings at the terminations : or

Blue : throughout their length . with Green & yellow : markings at the terminations :

* Bare conductors’ are painted or identified by a coloured tape , sleeve or disk ,

 

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Electrical Supply July 2009

a) Provision of supply
The supply into a hazardous area should be directly from a main switch isolator and not from a ring main feeding other parts of the site. The switch isolator must isolate all live and neutral conductors.

b) Type of Supply
The form of earthing defines the types of electrical supply used on a site.
* TT system, a system having one point of the source of energy directly earthed, the exposed-conductive-parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source;
* TN system, a system having one or more points of the source of energy directly earthed, the exposed-conductive-parts of the installation being connected to that point by protective conductors;
* TN-C system, a system in which neutral and protective functions are combined in a single conductor throughout the system;
* TN-S system, a system having separate neutral and protective conductors thought the system;
* TN-C-S system, a system in which neutral and protective functions are combined in a single conductor in part of the system;
* IT system, a system having no direct connection between live parts and Earth, the exposed-conductive-parts of the electrical installation being earthed.

For new installations the electrical supplies into a hazardous area should be TT, although TN-S, may be acceptable.

TN-C-S (PME) may only be used on existing installations subject to an
appropriate, documented, risk assessment being carried out and that the
installation is subjected to regular checks on the current on the diverted neutral
current. For these installations it may be more practical to install a “derived TT
system” for the equipment in the potentially hazardous area.
b) Cable sizing
All electrical power cables must be designed and sized by a competent electrician/designer.
The design and cable sizing needs to take into account a variety of factors including:
* Length of the cable(s),
* Proposed method of installation (e.g. underground buried, underground in duct, above ground on trays),
* Type of load (motors, heaters)
* The maximum load, (most LPG pump motors, especially single phase, take a high starting current),
* Current

Information on cable design is available from tables in the 17th Edition Electrical Regulations ,

c) Voltage
Tests should be carried out installations to confirm there are no excessive voltage drops. (e.g. due to length of cable, connections from the incoming supply to contactors/cables, contactors/switches.) The voltage drop to the extremity of the circuit should not exceed 5%; more information in BS7671.

The available voltage at any motor should remain within the tolerances specified by the motor manufacturer both for start up and during running.

d) Protection against Electric Shock
When a different type of supply is used for the hazardous area compared with the supply to other parts of the site there must be a suitable separation, typically in excess of 2.5 metres, between un-insulated components to prevent
inadvertent contact between the two.

e) Site Earthing
Site earthing is required for all sizes of storage vessel, when the installation is fitted with electrical equipment, the primary requirement being protection against electric shock. This is not the same as the earthing required for the dissipation of static electricity; see
5 i). Earthing figures for bonding should meet those given in BS 7671.

An earth-bonding conductor should be run back to a primary earthing point at the source of energy. For a TN-S system this is where all metallic parts will ultimately be bonded.

The electrical supply must have a suitable effective earth. A “split” earth bar and test socket should be installed for each installation to allow testing of the earthing efficiency.

Bonding to other services must be connected to earth and comply with BS7671.

Notes:
• The armour of SWA cable should not be used as an earth conductor.
• Installations using cathodic protection systems for corrosion protection of vessels or pipework require special consideration and expert advice should be sought. the current rating of the type, the type of load (e.g. motor, heater etc), its short circuit capability and earthing impedance values, which need to be evaluated on site to ensure compliance with BS7671.

g) RCDs
Every power circuits into potentially hazardous areas should be protected by a Residual Current Device (RCD) being capable of disconnecting all poles including neutral of the circuit having a disconnection time of not more than 30ms.

h) Generators
Special precautions are required when a generator is to be used either during normal operations or more importantly in emergencies (see BS7671).

5. Installation of Equipment
a) Motor overload/low voltage protection

BS 7671 requires that every electric motor having a rating exceeding 0.37 kW be provided with control equipment incorporating means of protection against overload of the motor. Every motor needs to be provided with means to prevent automatic restarting after a stoppage due to a drop in voltage or failure of supply.

b) Cables
Cable conductors should only be of copper.
Power cables with integral mechanical protection are preferred, non-armoured cables can only be used providing the cable is protected by another method against mechanical damage.
Earthing cable sizes need to be assessed for each site prior to installation. 25mm2 should be adequate for most installations, should a smaller cable be considered then the appropriate calculations need to be carried out before installation.

c) Glands
Cable glands should be suitable for the relevant zone or area, the type of equipment being connected, the connection thread and for the cable being used. They should also maintain the Ingress Protection of the equipment.

d) Auxiliary equipment
Any auxiliary electrical equipment (e.g. solenoid valves) should be suitably protected (e.g. using an individual RCD) in the event of failure of the equipment. This protection should not be incorporated into hazardous area enclosures unless written approval is received from the manufacturer.

e) Enclosures of equipment for use in potentially Hazardous/Protected Areas
Any modification of the enclosures after dispatch from the manufacturer will invalidate the electrical certification for use in hazardous areas and must not be carried out.

f) Emergency Switch
A suitable switching device for emergency use should be fitted outside the potentially hazardous areas or separation distance (whichever is greater). When operated this would disconnect all electrical supplies (live and neutral conductors) to the associated equipment. It may be preferable to leave some auxiliary circuits live; e.g. lighting for the area, gas detection systems etc.

Except where failure to start after a brief interruption would be likely to cause greater danger; the installation should incorporate a system so that following the loss of power (e.g. power cut) power is not restored automatically but needs to be reset manually by an authorised person. This may be incorporated with the switching device in the above paragraph.

g) Isolation
Where required by BS7671 and BSEN60079–14 a means to secure the isolation in the off position shall be provided for the equipment in the potentially hazardous areas.

h) Switching off for mechanical maintenance
A means of switching off and isolating the power supply for mechanical maintenance should be provided for any electrical equipment in accordance with BS7671 and BSEN60079-14.

 

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i) Earthing
Earthing arrangements should be assessed for each site prior to installation. Metallic sections of an installation should be designed, installed and tested to confirm they are electrically connected. For equipment not mounted on common
steelwork each component may need to be electrically connected, using an appropriately sized conductor, back to a single point.
The use of electrical connections across mechanical joints is not necessary providing, after installation, electrical conductivity is checked and confirmed to be acceptable. This should be checked periodically at intervals not exceeding 2 years.

Consideration should be given as to whether earthing of metallic items within a distance of 2.5 metres is also required. e.g. adjacent metallic fencing. Care should be taken to ensure that surface features (e.g. powder coating) do not render surfaces insulating.

For installation the incorporate Cathodic Protection systems suitable measures will need to be taken to ensure the parts of the installation protected by the CP system are not connected to the electrical system earth. Electrical isolators (with static build up protection) may need to be incorporated into the installation.

system are not connected to the electrical system earth. Electrical isolators (with static build up protection) may need to be incorporated into the installation.

j) Static earthing
Before connecting a vessel to a local earth rod an assessment is required to see if this would affect the protection of the total installation. It may be necessary to supply a separate “clean” earth for a delivery tanker earth connection.

k) Sodium lamps
Due to the potential hazard of ignition if a lamp is dropped or falls sodium lamps should not be installed within or above zone 0 or 1 areas. Before changing such lamps above zone 2 areas the area should be checked to confirm there is no flammable atmosphere present.

l) Redundant cables or cores
Any redundant cables/cores should either be removed or terminated in a suitable enclosure.

m) Multistrand cables
To prevent loose strands the terminations of these cables should be fitted with crimped or similar ends.

6. Testing/documentation
a) Initial inspection
All new installations and equipment should be subject to a detailed inspection as part of the commissioning, suitable documentation should be issued on satisfactory testing of the installation. Typical information is given in Appendix 1.
On completion DSEAR requires a register of the electrical components, their relevant zone of installation and the equipment approvals. Typical register layout is given in Appendix 2

b) Periodic Inspection
This is the routine inspection of all equipment, systems and installations and information is given in BS EN 60079-17. An assessment should be made, and recorded, at the time of issuing the initial inspection of:

˃The type of inspections required usually visual or close
˃ The period between inspections.

installations these are normally 12 months but must not exceed 3 years)

Visual and close inspections can be carried out without removing any covers or isolating the power.
The results of all inspections should be recorded.

c) Detailed inspection
In addition to any other periodic inspections a detailed inspection should be carried out at intervals to be determined by the competent electrician (usually not exceeding 5 years) or after any modifications to equipment and/or wiring. Modifications being defined as any change to the wiring, circuits or the replacement of items that are not identical to the one removed.

The next electrical survey will be due no later than ------------ 12 months from the
date of this document. ---------- (Delete as applicable.)
Signed: -------------- Name: ------------
Date: ----------
Qualification for hazardous area work: -------------------

This Schedule relates only to Certificate/Report Reference

Cable type :
A ) PVC/PVC cables
B ) PVC cables in metal conduit
C ) PVC cables in non-metal conduit
D ) PVC cables in metal trunking
E ) PVC cables in non-metal trunking
F ) PVC/SWA cables
G ) XLPE/SWA cables
H ) Mineral Insulated cables
Other ?
Extent covered by this schedule

Stripping out of Redundant Installation

1) All redundant installations shall be stripped out as far as practical. Where this exercise could lead to any future confusion labels shall be installed giving clear concise instructions.

2) Where the stripping out of redundant installation is specified, the work shall be carried out with the same care and attention as for a new installation, and the Contractor shall ensure that no damage to the building fabric or equipment ensues.

3) Under no circumstances shall the Contractor allow any of his own, or any other Contractor’s or Sub-Contractors operatives to disconnect or cut a live cable, or cut conduit / trunking containing ANY cables.

 

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extract taken from wiring maters 2009

Conclusion
When carrying out additions or alterations to existing electrical installations, the reconfigured aspect of the electrical installation should comply with BS 7671:2008. The installer does not simply take responsibility for the newly installed or reconfigured element of the installation but all parts of the circuit(s) worked on - including the need to comment on the continued suitability or
otherwise of the equipment belonging to the distributor - this includes the condition of the metering equipment,
supply and meter-tails, distribution equipment and the earthing and bonding arrangements. If the client does not want to pay for
upgrades to existing equipment, this does not absolve the installer from responsibility, nor does a disclaimer.