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

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“ Rcd's “

Fire detection circuits must be supplied independently of other circuits and not protected by an Rcd protecting multiple circuits. 560.7.1 All circuits in a bath shower room must be protected by a 30mA RCD. P166, 701.411.3.3
Where applicable an RCD notice must be fixed on or next to the CCU 514.12.2 An RCD should not be used as a main switch 314.2 If the maximum Zs values for a circuit in a TN systems cannot be met, the circuit may be protected by a 30mA RCD. 531.3.1
If the maximum Zs values for a TN systems cannot be met, the installation may be protected by an 100mA RCD and treated as a TT systems . 531.3.1 : 411.5.1 : 411.5.2 : 411.5.3
Unless specifically labelled or suitably identified, all 13A socket outlets must be protected by a 30mA Rcd. 411.3.3
In a TN systems , the part of a lighting circuit in a bath or shower room is required to be 30mA RCD protected. 411.3.3 , 701.411.3.3

Where a cable is buried in a wall or partition at a depth of less than 50mm on either side it must be sufficiently mechanically protected against penetration OR RCD protected AND installed either horizontally within 150mm of the top of the wall or vertically within 150mm of the angle formed where two walls meet or run horizontally or vertically to an accessory, luminaire or CCU 522.6.6 , 522.6.7 . This applies to a cable in a partition constructed using metallic parts other than fixings irrespective of the cable depth. 522.6.8

Surface run cables do not require RCD protection. OSG p22

A single RCD protecting a TT systems must be installed at the origin of the installation unless the part of the system between the origin and the RCD fulfils the requirements for protection by Class 11 equipment or equivalent insulation 531.4.1

All Electrical equipment must be accessible for operation , inspection & testing maintenance and repair. 132.12

Rcd Test Procedure

Many RCD test meters have a facility where tests can be carried out during the positive or negative half of the supply cycle. For tests 1 & 2 the RCD operating time to be recorded is the longer of the two measured during the half cycle tests.

DO NOT press the test button on the RCD before testing as this can temporarily reset a faulty RCD

Test 1
Adjust the current setting on the test meter to 100% of the rated trip current of the RCD and perform a test. A general purpose BS4293 RCD should operate within 200mS . A general purpose BS-61008 RCD or RCBO to BS-61009 should operate within 300ms

Test 2
An RCD provided for Basic Protection should have a rated TRIP current not exceeding 30mA If the RCD is rated at 30mA , adjust the current setting on the test meter to 150ma ( x5 ) and perform a test. The RCD must operate in a time not exceeding 40mS.
Test 3
Adjust the current setting on the test meter to 50% of the RCD trip current and perform a test. The RCD should not operate within 2 seconds
The Test Button : Finally operate the RCD by pressing its test button

 

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Periodic Inspection Report :
Guidance for Recipients ( to be appended to the Report )

This periodic Inspection Report form is intended for reporting on the condition of an existing electrical installation ,

You should have received an original Report and the Contractor should have retained a duplicate .
If you were the person ordering this Report , but not the owner of the installation , you should pass this Report , or a copy of it , immediately to the owner ,

The original Report is to be retained in a safe place and be shown to any person inspecting or undertaking work on the
Electrical installation in the future , if you later vacate the property , this report will provide the new owner with details of the condition of the electrical installation at the time the report was issued ,

The ” Extent and Limitations “ box should fully identify the extent of the installation covered by this report and any limitations on the inspection and tests , the contractor should have agreed these aspects with you and with any other interested parties ( Licensing Authority , Insurance Company , Building Society etc ) before the inspection was carried out .

The report should identify any departures from the safety requirements of the current Regulations and any defects , damage or
Deterioration that affect the safety of the installation for continued use , FOR ITEMS CLASSIFIED AS “ REQUIRES URGENT ATTENTION “ THE SAFETY OF THOSE USING THE INSTALLATION MAY BE AT RISK ,
And it is recommended that a competent person undertakes the necessary remedial work without delay .

For safety reasons , the electrical installation will need to be re-inspected at appropriate intervals by a competent person . the maximum time interval recommended before the next inspection is stated in the Report under “ next Inspection “

The Report is only valid if a Schedule of inspections and a Schedule of Test Results are appended ,

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE :

Guidance for Recipients ( to be appended to the Certificate )

This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed , constructed , inspected and tested in accordance with British Standard 7671 ( IEE Wiring Regulations )

You should have received an original Certificate and the contractor should have retained a duplicate Certificate .
If you were the person ordering the work , but not the owner of the installation .
You should pass this Certificate , or a full copy of it , immediately to the owner .

A separate Certificate should have been received for each existing circuit on which minor works have been carried out , this
Certificate is not appropriate if you requested the contractor to undertake more extensive installation work , for which you should have received an Electrical installation Certificate

The “ Original Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the Electrical installation in the future , if you later vacate the property , this Certificate will demonstrate to the new owner that the minor Electrical installation work carried out complied with the requirements of British Standard 7671 at the time the
Certificate was issued ,

Dual Supply : ( 514.15.1 )

When an installation includes a generating set that can be employed as an alternative source of supply in parallel with another source , a label having the wording shown below should be fixed at or near :

(1) the origin of the installation :
(2) the meter position , if remote from the origin :
(3) the consumer unit or distribution board to which the generating set is connected :
(4) all points of isolation of both sources of supply :

WARNING

Isolate both mains and on-site generation before carrying out work :
Isolate the mains supply at …………………………………………..
Isolate the generator at ………………………………………………

External Influences :
( 611.2 ) any known changes in external influences , building structure , and alterations or additions which may have affected
The suitability of the wiring for its present load and method of installation should be noted ,

Note : should also be made of any alterations or additions of an irregular nature to the installation , if unsuitable material has been used , this Report should indicate this together with reference to any evident faulty workmanship or design ,

 

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Caravan Installations : Part 7 , Special Installations or Locations

( 721.514.1 )
All Caravans and Motor Caravans should have a Notice fixed Near the Main Switch Given Instructions on the Connection and Disconnection of the Caravan Installation to the Electricity Supply

The Notice should be of a Durable Material Permanently fixed , and bearing in Indelible and easily Legible Characters the text shown in BS-7671 Regs : p-211 / fig 721 :

The Inlet shall be Installed :

(i) Not more than 1.8m above Ground Level ,
(ii ) In a Readily Accessible Position ,
(iii) In an Enclosure with a Suitable Cover on the Outside of the Caravan ,

721.537.2.1.1.1

A notice of Durable Material shall be Permanently fixed near the Main Isolating Switch inside the Caravan .
Bearing the Text shown in 721 in the Appropriate Language(s) in Indelible and Easily Legible Characters :

" Remember " any Alterations on Caravans look at this Page Regs : 213

Main Equipotential bonding ( 6mm2 ) ← required from the Main Earthing Terminal to Structural Metallic Parts such as Chassis . which will be Accessible from within the Caravan .

Notes to Table 3.3 / GN-3 * ( 1)
Test : ………………………………… Recommendation :

Protective …………………………….. Between the Earth Terminal of Distribution boards to the following
Conductors …………………………… Exposed-Conductive-Parts :
Continuity ………………………….. * Socket-Outlet Earth Connections ( note 4 )

Bonding …………………………….. * all Protective Bonding Conductors
Conductors ………………………… * all Necessary Supplementary Bonding Conductors
Continuity

Ring Circuit ………………………… where there are proper Records of Previous tests , this test may not be Necessary .
Continuity ………………………….. this test should be carried out where Inspection / Documentation indicate that there may
……………………………………… have been changes made to the Ring Final Circuit

Insulation …………………………… if Tests are to be made :
Résistance …………………………… * between Live Conductors, with Line(s) and Natural Connected
……………………………………….. together, and Earth at all final Distribution boards
…………………………………….. * at Main and Sub-Main Distribution panels, with Final Circuit Distribution boards
Isolated from mains ( note 6 )

Polarity ……………………………. At the following positions :
……………………………………... * Origin of the Installation
……………………………………... * Distribution Boards
……………………………………... * Accessible Socket-Outlets
……………………………………... * Extremity of Radial Circuits ( note 7 )

Earth Electrode ……………… Test each Earth Rod or group of Rods Separately, with the Test links Removed
Résistance ……………… and with the Installation Isolated from the Supply Source .

Earth Fault Loop …………….. At the following Positions :
Impedance …………………… * Origin of the Installation
……………………………….. * Distribution Boards
……………………………….. * Accessible Socket-Outlets
……………………………….. * Extremity of Radial Circuits ( note 8 )

Functional Tests
RCDs ……………………….. Tests as required by Regulation ( 612.13.1 ) followed by Operation of the Functional test button ,

Circuit-Breakers, ……………. Manual Operation to prove that the device(s) Disconnect the Supply .
Isolators and

Notes to Table 3.3 / GN-3 * ( 2 )

(1) The person carrying out the testing is required to decide which of the above tests are appropriate by using their experience and knowledge of the installation being inspected and tested and by consulting any available records :
(2) Where sampling is applied , the percentage used is at the discretion of the tester . however a percentage of less than 10 per cent is inadvisable
(3) The tests need not be carried out in the order shown in the table .
(4) The earth fault loop impedance test may be used to confirm the continuity of protective conductors at socket-outlets and at accessible exposed-conductive-parts of current-using equipment and accessories .
(5) Generally , accessibility may be considered to be within 3 m from the floor or from where a person can stand .
(6) Where the circuit includes surge protective devices ( SPDs ) or other electronic devices which require a connection to earth for functional purposes , these devices will require disconnecting to avid influencing the test result and to avoid damaging them .
(7) Where there are proper records of previous tests , this test may not be necessary .
(8) Some earth fault loop impedance testers may trip RCDs in the circuit .

Earth Fault Impedance : GN-3

Where protective measures are used which require a knowledge of earth fault loop impedance , the relevant impedance should be measured , or determined by an equally effective method .

Earth Fault Loop Impedance tests should be carried out at the locations indicated below :

(1) Origin of the Installation
(2) Distribution Boards
(3) Accessible Socket-Outlets
(4) Extremity of Radial Circuits

Domestic : 2392-10 ( 100A BS-1361 Type II / Max 50A MCB : Max ( 16ooo. kA ) to BS-7671

Continuity of Protective Conductors :

This test is of great importance and arguably the most important of them all for many reasons , despite of this fact at times shortcuts are taken and things are over looked .

Many electrical contractors who carry out testing very rarely understand the reasons for doing such a test , and the acceptable results obtained .

In this section we will not only be showing you how to conduct the test but the reasons for doing it ,
And which method to choose for a particular installation / wiring system .

This is the first test to be conducted in the sequence of tests , the reason for doing it as the first test in the sequence is because of the possible rise in potential across different metallic items that could arise if the CPCs and bonding were not in place or disconnected when carrying out other tests . An example of this is when doing an insulation résistance test , this
Typically puts 500v dc through the system , if metallic items were not bonded , then it could rise to a dangerous voltage .

The Test :
Before we talk about the individual tests . there has been a lot of confusion around the little things that need doing prior to even picking up an instrument .

This test is only conducted on radial circuits ,
( Q ) “ do we or don’t we disconnect the main bonding conductors’ from the ( MET ) ?

(A) “ Well this dependent upon whether the installation is already connected to the supply . if it is an initial verification ( new installation ) then it is permissible to disconnect the protective and → ∫ Equipotential conductors OLD ∫ ←
We are now on the 17th Edition : Main Protective Bonding Conductors from the main earthing terminal to carry out this test ,

If the installation is an existing one ( periodic ) then testing , the protective and Main Protective Bonding Conductors
Must “ NOT “ be disconnected . if this is the case then a loop test may be conducted to verify the integrity of the system .

There are 3 different methods’ that can be used to carry out this test , and is dependent upon a number of factors ,
Ω is the protective conductor under test part of the final circuit or a sub-circuit ?
Ω is the protective conductor under test a bonding conductor ?
Ω does the circuit under test form part of a metallic wiring system ?

Test Method 1 :

Test method 1 uses the phase as a return lead , otherwise known as the ( R1 + R2 ) Method .
This is the most common Method used for final circuits . as in most final circuits , the phase conductor
Runs alongside a CPC conductor and this factor is utilised in the test .
“ Instrument to be used “
“ Low-Résistance-Ohmmeter “
“ Scale to be used “ Ohms Ωs
The low Résistance Ohmmeter is then connected at the most furthest point of the circuit , and a reading is obtained .
This reading is made up of the Résistance of the ( R1 ) Phase Conductor and the ( R2 ) Protective Conductor and is given the name ( R1 + R2 ) .

GN-3 Colum for Recording ( R1 + R2 ) on the Schedule of Test Results .

Method :
Before the test can begin . if the circuit to be tested is not isolated then follow the correct safe isolation procedures .
Step 1 :
A temporary link is made at the distribution board between the Phase & Protective Conductor Systems .
Important :
Null the leads . this is very important as the wander lead will add a considerable résistance to the instrument reading .
If your instrument does not have a null function . then simply subtract the résistance from the actual reading .

(Q) “ but I only want the résistance of the CPC , why am I bothering with the résistance of the Phase ?
(A) “ This method has many advantages , not only to this test , but to other future tests . the main one being we can use Phase Conductor as part of the circuit as it eliminates any awkward and possibly dangerous wander leads draping everywhere . also this ( R1 + R2 ) reading can be used for working out our Earth Fault Loop Impedance Value if we decided not to Measure it ,
Polarity of the circuit is also obtained at the same time , “

Important :
Don’t forget to remove the Link once the test is finished !!!!!!

 

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Test Method 3 :

Test Method 3 is used where a Metallic Enclosure forms all or part of the Protective Conductor .

It is highly possible that the Protective Conductor under Test forms part of a steel conduit trunking or similar .
If this is the case then a few problems arise . due to possible corrosion or loose joints . the protective conductor résistance
Could rise to unsafe levels .

Parallel paths will form if there is a separate CPC , this must also be taken into consideration .

Because of this there are 3 tests that can be carried out . Only one need be adopted , but they differ due to the difficulty of gaining an accurate reading and increasing severity with regard to current carrying capacity .
1.5 times the design current , with a maximum of 25A to be used . the résistance of the protective conductor can be calculated from ( R2 = V- A )
The résistance between any extraneous conductive part and the main earthing terminal should be 0.05Ω or less ;
We are now on the 17th Edition : ( OLD ) supplementary bonding ,
All Supplementary Protective Bonding Conductors if required should also have the same résistance .

The 3 Tests :
(1) A standard Ohmmeter test as indicated in method 1 or method 2 / R2 ) this will not exploit any high résistance joints in the enclosure , and if used after must be visually expected along the length of run
(2) Phase-Earth loop Impedance test can be carried out if it is thought by the inspector that the soundness of the system is questionable.
(3) if the protective conductor is suspect then a high current test can be used of around

The Maths Involved in the Test .
When doing an inspection and testing course it is highly likely that you will encounter some form of maths involved while
Learning about the tests . at the end of the day electricity is a form of physics which deals with Resistances Voltages & Currents .
The duty holder whom carries out the duty holder whom carries out the inspection & testing must have a knowledge of why he/she is doing it , what to expect of the readings from the instrument and how to interpret these readings

(Q) “ When conducting a Continuity of Protective Conductor test. What kind of calculations could we be asked ?

(1) The value of R2 can be found using method 1 above :
(2) The max length & actual length of the circuit under test can be found when applying method 1 & 2 above .
(3) Subtraction of the wander lead résistance form the reading in method 2 .

2392-10 Fundamental Inspection , Testing & Initial Verification
Q(1) Electrical Test probes must comply with standards set by ?
A(1) a – BS-7671 b – GN-3 c – Guidance Note GS-38 d – BS-EN 60598

Q(2) Which of the following statement is false . during Initial Verification Inspection shall be made to verify ?
A(2) a – equipment has a British Standard or other mark or certification furnished by the manufacturer .
A(2) b – equipment is correctly selected and erected .
A(2) c - equipment is not visibly damaged . A(2) d - equipment is functioning .

Q(3) The person carrying out Inspection and Testing must have ?
A(3) a – an inspection & test qualification . b – sound knowledge and experience relevant to the installation being inspected
A(3) c – both ( a ) and (b) d – a current wiring regulations qualification .

Q(4) Put the following tests in the correct sequence : 1-Phase Sequence 2-Insulation Résistance of non-conducting floors & walls 3-Earth Electrode Résistance 4-Protection by barriers and enclosures providing during erection ?
A(4) 2.4.3.1. A(4) 1.2.3.4. A(4) 1.3.4.2. A(4) 3.2.4.1.

Q(5) A “ Tong tester “ is used to measure ?
A(5) Current : Voltage : Résistance : Frequency :

Q(6) If the person ordering Installation work is not the user then it is recommended that copies of the Electrical Installation Certificate must be given to ?
A(6) 1- the person ordering the work , 2- the person ordering the work and the user , 3- the person ordering the work and the local building authority , 4- the user and the local building authority ,

Q(7) Faults within existing Installations which “ do not “ effect new additions to the installation ?
A(7) 1- are required to be noted if observed by engineer doing the new additions ?
A(7) 2- are required to be corrected by the engineer doing the new additions ?
A(7) 3- do not need to be corrected by the engineer doing the new additions ?
A(7) 4 – are required to be reported to the local building authority by the additions ?

Q(8) when testing continuity of a ring final circuit wired with 2.5 / 1.5 pvc / pvc conductors using “ method 1 “ the value of ( R1 ) is 0.4Ω what should be the approximate value of ( R2 ) ?
A(8) a – 0.60Ω b – 1.00Ω c – 0.67Ω d – 0.16Ω

Q(9) the prospective short-circuit between line & neutral is measured at ( 900A) the maximum balanced prospective short-circuit current level between lines, as a rule of thumb , can be assumed to be approximately ?
A(9) a – 0.9kA b – 9 kA c - 90 kA d – 1.8 kA

Q(10) testing of CPCs is the testing of ?
A(10) a - insulation résistance b – continuity of main bonding conductors c - continuity of protective conductors d – earth fault loop impedance

Q (11) an instrument called a “ check box “ is sometimes used when ?
A(11) a – calibrating test instruments b – checking instrument battery voltage ? c – testing earth continuity d – comparing test results

Q(12) records of all checks , inspections & tests to an installation should be kept ?
A(12) a – for one year b – for 3 years c – for 10 years d – for the working life of the installation .

Q(13) when testing insulation of floors & walls the insulation must be able to withstand a test voltage ( a.c. rms ) of at least ?
A(13) a – 0.5kV b – 1.0kV c – 2.0kV 4.0kV

Q(14) IEE Guidance Note 3 recommends that for reliability on service the résistance of any Earth Electrode should be below ?
A(14) a – 0.35Ω b – 0.8Ω c - 100Ω d- 200Ω

Q(15) defects or omissions revealed during Initial Verification shall ?
A(15) a - be made good when the certificate is issued b - be made good after the certificate is issued
c - be made good within 30 days of the certificate being issued d - a - be made good before the certificate is issued

Q(16) the responsibility for comparing test results with relevant criteria during the verification of a new installation lies with ?
A(16) a – the design engineer b – the installation engineer c – the test engineer d – the client

Q(17) if the highest reading for ( r1 + r2 ) recorded while testing the continuity of ring final circuit conductors is 0.9Ω ,
What will be the value of ( R1 + R2 )
A(17) a – 1.8Ω b – 0.9Ω c – 0.45Ω d – 0.225Ω

Q(18) control gear and interlocks should be operated when carrying out ?
A(18 ) a – functional testing b – isolating testing c – polarity testing d – continuity testing .


PS – you will get the answers ,

 

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Q19 - Table 9A in the On Site Guide gives a value of 19.51 (mΩ/m) for a line conductor of 2.5mm2 and a protective conductor of 1.5mm2. What would be the resistance of a circuit 25m in length when wired using these conductors:
A(19) a - 4.87 Ω. B - 487 Ω. C - 780 Ω. D - 0.487 Ω.
Q20 - If defects on an existing installation are found when carrying out alterations or additions the person responsible for issuing the ‘minor works certificate’ shall:
A - record the defects on the certificate so far as is reasonably practicable.
B - always record the defects on the certificate.
C - repair the defects before issuing the certificate.
D - record the defects on a separate document.
Q21 - Which of the following is ‘not required information’ which should be made available to the inspection and test engineer:
A - the maximum demand expressed in Amperes.
B - the name of the manufacturer of the electrical components .
C - the nature of the load current.
D - the type of earthing arrangement.
Q22 - For basic and fault protection using SELV and PELV systems, which of the following requirements is true:
A - The nominal voltage must not exceed 50V a.c. or 120V d.c.
B - The nominal voltage must not exceed 110V a.c. or 120V d.c.
C - The nominal voltage must not exceed 110V a.c. or 50V d.c.
D - The nominal voltage must not exceed 120V a.c. or 110V d.c.
Q23 - When carrying out an earth fault loop impedance test on a circuit the value for (R1 + R2) was found to be 0.3 Ω. A value for Ze was already recorded as 1.15 Ω. The value for Zs can be assumed to be:
A - 0.85 Ω. B - 1.15 Ω. C - 1.45 Ω. D - 1.18 Ω.
Q24 - Which of the following does not meet the requirements for maximum value of voltage drop on a 230V supply, supplied directly from a public low voltage system, as stated in Appendix 12 of BS 7671:
A - Lighting 5.9V; Sockets 8.2V.
B - Lighting 3.5V; Sockets 11.7V.
C - Lighting 6.8V; Sockets 5.3V.
D - Lighting 4.0V; Sockets 5.7V.
Q25 - Instrument calibration certificates are normally valid for:
A - 3 months. B - 6 months. C - 1 year. D - 2 years.
Q26 - The maximum prospective fault current recorded on an electrical installation certificate should be:
A - the greater of either the short-circuit current or the earth fault current.
B - the lesser of either the short-circuit current or the earth fault current.
C - the short-circuit current.
D - the earth fault current.
Q27 - When completing an installation certificate under ‘Number and Type of Live Conductors’, the 3-phase, 4-wire box should be ticked if the supply is:
A - 2-phase, neutral and earth.
B - 3-phase, and earth.
C - 3-phase and neutral.
D - four single phase supplies.
Q28 - When completing a Minor Works Certificate, which of the following is not an example of an ‘essential test’:
A - Prospective fault current. B - Earth fault loop impedance.
C - Insulation resistance. D - Polarity.
29 - Regional electricity companies quote a maximum likely value of external loop impedance (outside the consumer’s installation) for a TN-S system as:
A - 0.35 Ω. B - 0.8 Ω. C - 21 Ω. D - 200 Ω.
Q30 - A visual inspection of a new installation must be carried out:
A - upon completion
B - during testing
C - during erection
D - during erection and upon completion

 

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C&G 2392-10 Fundamental Inspection, Testing and Initial Verification - Paper 4 :

Q1 - Low-resistance ohmmeters used for continuity measurements should have a no-load voltage and a short-circuit current of :
A(1) a - Voltage between 4V and 24 V; short-circuit current of 200 mA.
A(1) b - Voltage between 0V and 24 V; short-circuit current of 100 mA.
A(1) c - Voltage between 4V and 20 V; short-circuit current of 1 mA.
A(1) d - Voltage between 0V and 20 V; short-circuit current of 1 mA.
Q2 - The protective measure where basic protection is provided by insulation of live parts, barriers or enclosures and fault protection is provided by simple separation of the separated circuit from other circuits and from earth is called:
A(2) a - earth free equipotential bonding.
A(2) b - additional protection.
A(2) c - prevention of mutual detrimental influence.
A(2) d - electrical separation.
Q3 - When taking impedance measurements at ambient temperature a ‘Rule of Thumb’ correction factor may be applied to take into account the increased resistance of conductors due to load current. The recommended correction factor as indicated in BS7671 Appendix 14 is : ( hint ) p-361
A(3) a - 0.5. b - 0.75. c - 0.8. d - 1.2.
Q4 - The metal sheath of the supply cable is used as part of the earth return path in which of the following systems:
A(4) A - TT. B - TN-C. C - TN-S. D - TN-C-S.
Q6 - Which of the following statements is correct regarding double insulation being used for both basic and fault protection:
A(6) a - Basic protection is provided by basic insulation and fault protection is provided by supplementary insulation.
A(6) b - Fault protection is provided by basic insulation and basic protection is provided by supplementary insulation.
A(6) c - Basic protection is provided by both basic insulation and supplementary insulation.
A(6) d - Fault protection is provided by basic insulation and supplementary insulation.
Q7 - Put the following tests in the correct sequence: 1-earth fault loop impedance 2-phase sequence 3-prospective fault current 4- voltage drop:
A(7) a - 1.3.2.4. b - 2.4.1.3. c - 1.4.3.2. d - 4.1.2.3.
Q8 - Which of the following IP Codes signifies protection against total immersion in water:
A(8) a- IP 4X. b - IP 8X. c - IP X4. d - IP X8.
Q9 - An insulation resistance tester must be capable of delivering a test current of not less than:
A(9) a - 0.5 mA. B - 1.0 mA. C - 2.0 mA. D - 20 mA.
Q10 - The proposed interval between initial verification and the first periodic inspection should be recommended by:
A(10) a - the person carrying out the initial verification. b - the person who designed the installation.
c - the installation engineer. d - the client .
Q11 - Which of the following does not meet the requirements for maximum value of voltage drop on a 400V supply, supplied directly from a public low voltage system, as stated in Appendix 12 of BS 7671:
A(11) a - Lighting 11.1V; Sockets 19.6V. b - Lighting 4.7V; Sockets 22.3V.
c - Lighting 6.8V; Sockets 11.4V. d - Lighting 10.9V; Sockets 15.5V.
Q12 - Which of the following is not a method of ascertaining the prospective short circuit current at the origin of an installation:
A(12) a - Measurement. b - Calculation. c - Enquiry. d - Elimination.
Q13 - The test current applied to a 30mA RCD to check for a 40ms maximum disconnection time is:
A(13) a - 15mA. b - 30mA. c - 150mA. D - 300mA.
Q14 - Which of the following protection devices is unlikely to be suited for short circuit currents in excess of 6kA:
A(14) a - BS 3036 semi-enclosed fuse. B - BS 1361 cartridge fuse.
c - BS 88 general purpose fuse. d - BS EN 60898 circuit breaker.
Q15 - Which of the following statements is true:
A(15) a - A non-conducting location should contain protective conductors.
b - A non-conducting location should contain no protective conductors.
c - A non-conducting location should contain bonding conductors only.
d - A non-conducting location should contain extra-low voltage conductors only.
Q16 - When testing continuity of a ring final circuit wired with 2.5/1.5 PVC/PVC conductors using ‘Method 1’. The value of R1 is 0.8Ω, what should be the approximate value of R2 :
A(16) a - 1.20 Ω. B -2.00 Ω. C -1.34 Ω. D - 0.32 Ω.
Q17 - When using ‘protection by electrical separation’ the verification of live parts from those of other circuits and from Earth shall be confirmed by:
A(17) a - Earth continuity testing. b - Polarity testing. c - Functional testing. d - Insulation resistance testing.
Q18 - Which of the following is not permitted for use as an earth electrode:
A(18) a - Underground structural metalwork. B - Metal water mains pipes.
c - Lead sheaths of cables. d - Earth plates.
Q19 - When using a four terminal earth electrode tester to measure earth electrode resistance the connection to the earth electrode is made using terminals:
A(19) a - C1 and P1. b - C2 and P2. c - C1 and P2. d - P1 and C2.
Q20 - If the highest reading for (r1 + r2) recorded while testing the continuity of ring final circuit conductors is 1.2 Ω, what will be the value of (R1 + R2):
A(20) a - 2.4 Ω. B - 1.2 Ω. c - 0.6 Ω. d - 0.3 Ω.
Q21 - When subjecting a 30mA RCD to a test current of 150mA the protective conductor potential must not rise above a value of:
A(21) a - 50 V. b - 55 V. c - 110 V. d - 230 V.
Q22 - Which of the following tests would not normally be required during initial verification of an electrical installation:
A(22) a - RCD testing. b - Prospective fault current. c - Continuity of main bonding conductors. d - Verification of voltage drop.

Q23 - During earth loop impedance testing Ze is measured with the main bonding conductors disconnected whilst a live Zs test is carried out with the bonding conductors connected. This often leads to unexpected readings whereby the value of Zs can be lower than Ze. This is normally assumed to be because of:
A(23) a - parallel earth paths during the Zs test. b - parallel earth paths during the Ze test.
c - less conductor distance during the Zs test. d - less conductor distance during the Ze test.
Q24 - During initial verification of a TN system the installation earth conductor was recorded as 16mm2. The minimum size of main bonding conductor should be:
A(24) a - 4mm2. b - 6 mm2. c - 10 mm2. d - 16 mm2.
Q25 - When carrying out an earth fault loop impedance test on a circuit the value for (R1 + R2) was found to be 0.4 Ω. A value for Ze was already recorded as 1.2 Ω. The value for Zs can be assumed to be:
A(25) a - 0.4 Ω. b - 0.8 Ω . c -1.2 Ω. d - 1.6 Ω.
Q26 - During earth electrode resistance testing the current test spike is placed 30 metres from the earth electrode under test. The potential test spike is placed midway between the earth electrode and the current spike. The potential spike would then normally be moved a distance each way of approximately:
A(26) a - 1 metre. b - 3 metres. c - 6 metres. d - 15 metres .
Q27 - The prospective short-circuit current between line and neutral is measured at 850 A. The maximum balanced prospective short-circuit current level between lines, as a rule of thumb, can be assumed to be approximately:
A(27) a - 0.85 kA. b - 1.7 kA. c - 8.5 kA. d - 17 kA.
Q28 - The schedule of test results certificate shown in both BS 7671 and Guidance Note 3 requires completion of the:
A(28) a - (R1 + R2) and R2 columns . b - (R1 + R2) or R2 column.
c - (R1 + R2) columns only. d - R2 column only.
Q29 - During inspection, a circuit breaker to BS EN 60898 was seen to have a small rectangular box with the value 6000 marked within. This figure represents:
A(29) a - the current required to activate the device. b - the rated short-circuit capacity of the device in kA.
c - the current, in amps, expected during a short-circuit fault.
d - the rated short-circuit capacity of the device in Amps.
Q30 - When completing an Inspection Schedule, where an inspection was not carried out, the relevant box must be completed using a:
A(30) a - √ - NOW CLICK 'BACK' TO TRY AGAIN. b - X - NOW CLICK 'BACK' TO TRY AGAIN.
c - N/A - NOW CLICK 'BACK' TO TRY AGAIN. d - LIM - NOW CLICK 'BACK' TO TRY AGAIN.

 

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TN-C-S Systems
Not Allowed in Certain Locations i.e. Petrol Stations

( PME ) Important to Ensure that the Neutral is kept at Earth Potential by Earthing it at Many Points along its Length ( Hence “ Multiple “ Earthing )

If this is Not done “ a Fault to Neutral in One Installation could Cause a Shock Risk in all the Other Installations Connected ,

Concentric Cable : Single Core Cable Armouring , ( PEN ) Line / Neutral & Earth Combine ,
Single-Phase Split Concentric Cable with Stranded Copper Phase Conductors and Copper Wire Neutral & Earth Continuity Conductors 600 / 1000V

Domestic Inspection & Testing : 2392-10

( 612.9 ) Where Protective Measures are used which Require a Knowledge of Earth Fault Loop Impedance , the Relevant Impedance shall be Measured . or Determined by an Alternative Method :

External Earth Fault Loop Impedance , ( Ze )

( Safe Working Procedure ) Regulation ( 12 ) “ EAWR – 1989 “ ≈ ≈ ≈ ( Lock Off ) ≈ ≈ ≈

( Caution !! Electrician at Work do Not Switch On )

The First off Our ≈ Live Tests ≈ is ( “ Earth Fault Loop Impedance “ ) Determing External : Ze ←
This is a ( Live Test ) Which Can only be Measured by Testing as Near as Possible to the Origin of the Instillation

The Earthing Conductor has to be Disconnected from the Earthing Terminal ( 16mm2 ) to Eliminate Parallel Paths on the Installation Side ,
There for It is Essential for Safety Reasons for the Entire Installation to be Isolated form the Supply before doing this ,

Instrument : No-Tip Loop Tester :

3 – Leads Used ,

Green Lead Onto the Main Earthing Conductor Which is Disconnected : ← 1st
Blue Lead Onto the Supply Side of Main-Switch , ← 2nd
Brown Lead Onto the Supply Side of Main-Switch ,

Turn the Instrument On : This will Give me the “ Voltage “ ( and the “ Polarity “ is Correct : 241V Press the Loop Test : 0.66Ω *
Transformer Must be Quiet a Distance away ,

It is Good Practice to Repeat the Test Again ← ← ←

Green Lead Onto the Main Earthing Conductor Which is Disconnected : ← 1st
Blue Lead Onto the Supply Side of Main-Switch , ← 2nd
Brown Lead Onto the Supply Side of Main-Switch ,

Turn the Instrument On : This will give me the “ Voltage “ and the “ Polarity “ is Correct : 242V Press the Loop Test : 0.66Ω

Take the Highest of the Two Readings : ( 0.69Ω ) *

Re-Connect the Earthing Conductor back Onto the Terminal

I’ll be Recording this in the box , I’ll be putting This Onto the Test Certificate ( Schedule of Test Results )

It’s a Good Idea to take a Photo-copy of Certificate on site , any Alterations can be put Onto the ( Original Schedule of Test Results ) at Home

Archive for the '2391 - how to test' Category

Continuity of Final Circuit Conductors – Radial
Please note that this is a dead test and the circuit must be isolated when testing
Top be carried out on radial circuits to ensure the CPC of the circuit is undamaged and connected throughout the circuit
The highest reading should be obtained from the furthest part of the circuit. If the highest reading appears not to […]

September 2nd, 2008 | Posted in 2392 – how to Test / No Comments

Continuity of Bonding Conductors :
1. Safely isolate the supply
2. Disconnect one end of the conductor, preferably the end at the consumer unit.
3. (Null out test leads) or ( record and remember to subtract from end result)
4. Connect one test lead at the consumer unit’s disconnected end
5. Connect the other test lead to the metal work of which the conductor […]

September 2nd, 2008 | Posted in 2391- how to Test / 2 Comments

Test 1B Testing – Continuity of the Protective Conductors :
Description of test
Performing this test is to ensure that there is continuity throughout the circuit, that there are no breakages and conductors have been connected correctly. Be sure you have isolated the supply before beginning the test.

Methods
Test method 1 : Short lead Test
Test method 2 : Long lead Test

Test Equipment
Low Ohm Resistance Ω

PFC : 2391-

Perspective fault current
1. This is a live test
2. set Instrument to PFC test
3. Place one probe on the incoming Neutral conductor
4. Place the other probe on the incoming Line conductor
5. Test and record result
Note: some three lead tests will need the 3rd test lead to be connected to the main earthing terminal

Insulation Resistance Testing : 2391-

an insulation resistance test is like a pressure test of the circuits. On a 230v circuit, a test voltage of 500 volts is sent down. We do this test to check for current leaks in the insulation, hence “insulation resistance test”. Current leaks could occur from anything such as old age to crushed cables
Information to consider when doing an insulation resistance test
- As 500v volts is being sent down the circuit, if the building is occupied , then all must be informed
- Remember to remove all lamps for fittings because lamps could blow and effect readings
- if it is not possible to remove a lamp from a fitting, ensure the switch is open
Ensure
- dimmer switches are removed (why?)
- Accessories with neon indicator lamps are switched off (why?)
- Pir’s are removed (why?)
- All fixed equipment isolated (ovens, TV’s, why?)
- Shaver sockets removed (why?)
- Electrical portable items are unplugged (why?)
1. Safely isolate the supply
2. remove equipment mentioned above
3. Set insulation resistance tester to 500v
4. Set instrument to 200Mohms if it is not self ranging
5. Test between Neutral & Line
6. Test between Line & CPC
7. Test between Neutral & CPC
note: lighting circuits should be tested with the switches on and while operating all 2 way switching in both positions.
note: If testing the whole board at the tails then you need the supply to the board OFF i.e. its main switch and tails de-energised and the board’s main switch in the ON condition.
note: If the supply to the board cannot be removed just lock the main switch off at the board and test the whole installation from the switched side of the isolator. (Now dead/use proving unit before and after

Earth electro Test : 2391-

Note: this is a live test
1. Safely isolate installation
2. Ensure the earth electro is connected to the main earthing terminal
3. Disconnection main earthing
4. Connect one probe of the earth loop impedance tester to the main disconnected earthing conductor
5. Use the other probe to connect to the incoming side of the Line conductor
6. Perform Test and record result
7. Reconnect Main earthing terminal

Earth Fault loop impedance Test Ze : 2391-

note: This is a live test
Ze can be remembered as Z external (Ze)
1. Safely isolate supply
2. Disconnect the earthing conductor
3. Set test metre to loop test (20 ohms)
4. One test probe shall be placed on the incoming Line conductors
5. The other test probe shall be connected to the disconnected main earthing conductor (3 lead test shall be referred to the manufactures manual, in some cases the 2 leads (green & black) shall be connected to each other
6. Test and record result
7. Reconnect the earthing conductor
( Zs= Ze + ( R1+R2 )

Dead Polarity Test : 2391-

- Polarity testing is to ensure that all protective devices are connected in Line conductors of the circuit
- If the test “continuity of circuit protective conductors” has already been completed. Then polarity has been correctly proved
1. Safely Isolate Circuit
2. The circuit you are testing for polarity shall have the CPC & Line conductors cross-connected at the origin of the circuit (Consumer Unit)
3. At the furtherest point of the circuit you are testing, a test shall be made between the CPC & Line. This means if testing ed a cooker, the switch should physically removed and tested on the incoming side of the switch.
4. A further check should be made, by removing the cross connected CPC & Line conductors at the Consumer Unit and performing the same test again (the reading should be high as the circuit is open). This shall proved that you are testing the correct circuit.
note: this test can be preformed at the ceiling rose on a light circuit, or at the switch

 

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Continuity of Ring Final circuit conductors – Ring : 2391-

note: To ensure the cables form a complete ring throughout and that every point is correctly connected in the correct polarity and has no interconnections
1. Safely isolate supply
2. Test continuity between the ends of the Line conductor and record value
3. Test continuity between the ends of the Neutral conductor and record value
4. Test continuity between the ends of the CPC conductor and record value
5. Join leg 1 of Line to leg 2 of Neutral
Now test between leg 2 of Line and leg 1 of Neutral
Note: that the resistance will be double of the single line conductor
6. Now join both legs which you just tested from
leg 1 of Line and leg 2 of Neutral joined
leg 2 of Line and leg 1 of Neutral joined
Testing between the jointed legs should give a reading of a half of the line conductor
7. Leave ends joined as in step 6
8. Test at each socket of the circuit between Line and Neutral note: all readings should be the same
Readings which tend to higher may have incorrect polarity at one of the sockets, but further investigation should proceed.
10. Repeat step 10 using CPC and Line
leg 1 of Line and leg 2 of CPC joined
leg 2 of Line and leg 1 of CPC joined
Record results
note: If there are any spurs on the circuit, it will be more than likely that the readings of them are the highest, and these ones should be recorded for your r1 + r2

Continuity of bonding conductors : 2391-

1. Safely isolate the supply
2. Disconnect one end of the conductor, preferably the end at the consumer unit.
3. (Null out test leads) or ( record and remember to subtract from end result)
4. Connect one test lead at the consumer unit’s disconnected end
5. Connect the other test lead to the metal work of which the conductor you are testing is connected to (ensure any painted metal work has been scratched off, to make a solid connection) by not connecting it to the clamp will prove that the integrity of that clamp is efficient enough/correct BS 951
6. Test
- the result will give the total resistance of the conductor (remembering to subtract the test lead resistance, if not previously nulled out)
7. Re connect bonding conductor

Live Polarity Test 2391-

Note: An approved voltage indicator shall be used or test lamp to GS38
1. This is a live test
2. Using the approved voltage indicator, one probe shall be placed on the incoming neutral, and the other on the incoming line conductor, on the main breaker. The indicator should how it is live
3. One probe shall now be placed on the CPC and the other on the incoming line conductor. The indicator should show it is live
4. A test shall be preformed between CPC & incoming neutral. The indicator should indicate that it is not live
Note: If the indicator produces results different to expected results above, the further investigation shall be taken

Continuity of Final circuit conductors – Radial : 2391-

Please note that this is a dead test and the circuit must be isolated when testing
Top be carried out on radial circuits to ensure the CPC of the circuit is undamaged and connected throughout the circuit
The highest reading should be obtained from the furthest part of the circuit. If the highest reading appears not to be at the end of the circuit, then further investigation should proceed (It maybe because of how the circuit was installed, although one end may appear to be closer to the CU than other points, it may still be the end of the circuit)
1. Safely isolate supply
2. Cross connect the Line and CPC at one end of the circuit, preferably at the consumer unit
3. At each point of the circuit, a test should been made between Line and CPC
4. The highest reading will determine the R1 + R2 value of the circuit
note: when the Line and CPC conductors are the same size, the total resistance can be simply divided by 2 to find the resistance of just the CPC
In most cases Twin & Earth is used and the size of the CPC is smaller than the Live conductors, therefore this equation should be used to determine the size of the CPC.
eg. Total resistance r1 + r2 = 0.35 ohms
r2= 0.35 x (2.5/(2.5+1.5))

Criticism :

The final ring-circuit concept has been criticized in a number of ways, and some of these disadvantages could explain the lack of widespread adoption outside the United Kingdom.
The only way to see the pros and cons of ring circuits is to compare them to the other option: radials.
Fault conditions are not apparent when in use
Ring circuits continue to operate without the user being aware of any problem if there are fault conditions or installation errors that make the circuit unsafe:
• Part of the ring missing or loose connections result in 2.5 mm2 cables running above rated current at times, resulting in reduced cable life.
o Radials with a loose connection will overheat severely and be an immediate fire risk.
o Radials with a broken connection will not function (if L or N broken), or function with no safety earth connection (if Earth broken).
• Accidental cross connection between two 32 A rings means that the fault current protection reaches 64 A and the required fault disconnection times are violated grossly.
o Testing at installation addresses this.
• Ring spur installations encourage using three connectors in one terminal, which can cause one to become loose and overheat.
o The same situation occurs with both radial and ring circuits when branching off is used.
• Rings encourage the installation of too many spurs on a ring, leading to a risk of overheating, especially if spur cables are too long
Complexity of safety tests
Testing ring circuits takes 5–6 times longer than testing radial circuits .The installation tests required for the safe operation of a ring circuit are substantially more time consuming than those for a radial circuit, or electricians qualified in other countries may not be familiar with them.

Archive for the '2 way switching' Category

2 Way Lighting : FOR APPRENTICES ,
Here we’ll explain how to do 2 way lighting

o———o …………………….. 0—————-0 ↔ ( the dots are to stop drawing move ) Experiment !!!
………. 0—————————o

The diagram shows single colours only. In real life these wires would be covered by an outer protective sheath and would include a bare earth wire and would be called a cable.
Brown sleeving or tape would of been placed on the wires as shown to show

Steel Armoured Cable info -

Hello, just a little information about Steel Armoured Cable (SWA)
Steel Armoured Cable is protected by a sheath of galvanised steel. This makes it suitable for direct burial, cable ducting or it can be surfaced mounted without any further protection. It can be used for indoors and outdoors.
Steel Armoured Cable (SWA) Cores Colours 3-core / 4- core
* there’s some old ( 2-core still out there )

RCD main switch + MCBs ( Non-Split Boards :

Having a Consumer Unit with an RCD as a Main switch and just MCBs, not on a split board contravenes the regulations in the 17th Edition under reg, 314.1 (see also 314.2 )
An Rcd as a main switch when tripped due to the failure of a circuit or due to nuisance tripping will affect all other

The IEE recently published the 17th edition Wiring Regulations, (BS 7671), which came into force in
July 2008. Candidates are expected to have knowledge of the 17th edition wiring regulations, and
must answer questions accordingly.
The unit and complex numbers were amended from June 2008 onwards to signify that the
qualifications meet 17th edition requirements.

2391-01 became 2391-10
2391-02 became 2391-20
Unit 101 is now 301
Unit 102 is now 302
Unit 201 is now 303
Unit 202 is now 304

Other than the wiring regulation updates, the content of this qualification remains unchanged.
Important:
Candidates who have passed units under the old regulations (i.e. they already hold 101, 102, 201 or 202) do not need to re-sit under the new unit numbers.

 

[amberleaf]

Drawings and labels 2391- march 2009

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.
Page 8
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.

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.

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 theSchedules 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.

 

[amberleaf]

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.

Inspection & Testing Methods

Testing - Sequence of Tests : GN-3
1. Continuity of protective conductors ( 612.2.1 )
2. Continuity of Ring Final Circuit Conductors ( 612.2.2 )
3. Insulation resistance ( 612.3 )
*. Protection by SELV / PELV or by Electrical Separation ( 612.4 )
* . Basic Protection by barriers and enclosures ( 612.4.5 )
4. Insulation Résistance / Impedance of Floors & Walls ( 612.5 ) - look p-62
5. Dead ↔ Polarity ( 612.6 )
6. Earth electrode resistance (Ze) ( 612.7 )
* . Live Polarity of Supply
Test Following Installation being Energized

1. Earth fault loop impedance (Ze) (Zs) ( 612.9 ) 2. Additional Protection ( RCD 612.10 ) 3. Prospective fault current (PFC) ( 612.11 )
4. Functional testing ( 612.13 )

Domestic Inspection & Testing : 2392-10

Additional Protection by Residual Current Devices ,

( DANGER LIVE TEST )

Domestic Installations Installed to meet the Requirements’ of the 17th Edition
Are likely to have more than One Residual Current Devices , whether a Standard RCD or devices such as RCBOs
The effect of those devices need to be verified by appropriate Visual Inspection and Tests

Many Instruments these days do the full range of Test Automatically

* Plugging Into the Socket-Outlet from Instrument *

The First Test is Undertaking at the Rated Current of RCD so the Instrument Set to Times - ( x1 ) the RCD should Operate ( and it has - 7.6 mS )

For General Purpose RCDs to BS-4293 / Operating time Less than 200mS ( Remember BS- 200mS ) ← *
RCDs to BS-EN 61008 & BS-EN 61009-1 / Operating time below 300mS ( Remember BS-EN 300mS ) ← *

S / Type RCDs ( BS-EN 61008 - BS-EN 61009-1 ) Operating time between 130mS & 500mS ( Regs: p-243 – table 3A )

Circuit-Breakers : ( Regs: p-243 )

Type : B to BS-EN 60898 and the Overcurrent Characteristics of RCBOs to BS-EN 61009-1 ( fig 3.4
Type : C ( fig 3.5 / 61009-1
Type : D ( fig 3.6 / 61009-1

Time Delayed RCDs Operate between ( 200mS + 50% ---- 200mS + 100% )

It “ Not a Requirement ” of the Regulations am going to repeat the Test on both parts off the Supply Wave Form ( ≈ 0º / 180º ≈ )

Instrument Set RCD - on x1 ( 180º ≈ 8.7mS ) the One you Recording is the Longest of the 2 Times
The Next Part of the Test is the x5 times Current Test , for RCDs Not Exceeding 30mA ( Provide For Additional Protection Against Electrical shock )
With the x5 time Multiplier selected so that’s 5x 30mA which Equates to a Test Current of “ 150mA “ ( the RCD should Operate within 40mS
And it has ( Oº ≈ 5.5 mS ) both parts off the Supply Wave Form , the One you Recording is the Longest of the 2 Times

Although Not in the Regulations am going to do “ Half Current Test “ the RCD should Not Operate ( ½ 1 ) > 1999 mS
This Test helps to Check the Sensitivity of the device ,

The Test Button :

Following the Electrical Test procedure described above , each RCD should be Operated by means of its integral Test Facility .
This confirms that the device is responding to its design level of sensitivity and that all the mechanical parts are functioning .
The users of the Installations are advised ( by means of a notice at or near the origin of the Installations – Regs : 514.12.2 )



→ C&G 2392-10 Fundamental Inspection, Testing and Initial Verification - Paper 3 / 4
You’ll have the answers on Sun / Mon , ←

Domestic Inspection & Testing : 2392-10

Check of Phase Sequence and Verification of Voltage Drop ,

The 17th Edition introduced two new Test Requirements ( Part 6 ) the First is Checking Phase Sequence ,
Checking is for Installations with Multi-Phase Circuits Only , but shall be Verify that the Phase Sequence is maintained though the Installation ( 2392-10 So as we are Single Phase here This Test is Not Applicable )

The Second New Requirement is for Verification of Voltage Drop ( 612.14 ) which its not normally Required during Initial Verification because you should have the Design Information at hand it should take into account Voltage Drop so there’s no need to do it here

Low-Voltage Installation : 17th Edition , 3% Lighting / 5% Power

( 612.14 ) Two-Ways to Verify the Voltage Drop ← * (1) Evaluate the Voltage Drop by Measuring the Circuit Impedance :
* (2) Evaluate the Voltage Drop Using Calculations :

Evaluation of Voltage Drop by → Measuring ← Circuit Impedance : 2392-10 / 2391-20

( 612.14 ) Work Example , (1)

Suppose that it is desired to verify that the voltage drop does not exceed 5% in an existing single-phase 230V , 50 Hz radial circuit supplying a 20A heating load connected at the end of the circuit , the circuit is supplied directly from a distribution board at the origin of the installation , the line and neutral conductors of the circuit have thermoplastic ( pvc ) insulation and their résistance ( R1 + R2 ) is 0.3Ω when measured at ambient temperature ( say 20º C )

As the circuit rating does not exceed 100A and the supply frequency is 50 Hz , ( R1 + Rn ) may be taken to be the circuit impedance ( that is, inductive reactance may be ignored )

To evaluate the voltage drop . the measured value of ( R1 + Rn ) should be increased on the basis of the increase in conductor temperature due to load current , and then multiplied by the design current of the circuit ( Ib ) ← in the absence of better information , a correction factor of ( Cf 1.2 ) ← should be used to increase the conductor résistance in this case . this assumes an increase in conductor temperature from ( 20º C ) ( ambient ) to ( 70º C ) ( the maximum permitted operating temperature for thermoplastic insulated conductors )

The voltage drop ( Vd ) for the single-phase circuit in this example is therefore given by :
( Vd ) = measured value of ( R1 + Rn ) x 1.2 x ( Ib ) ←

Therefore ……. ( Vd ) = 0.3Ω x 1.2 x 20A = 7.2 V .

A voltage drop of 7.2V is equivalent to 3.13% ( given by 100% x 7.2 ÷ 230V )
It has therefore been verified that , in the case of this example , the voltage drop in the circuit does not exceed ( 5% ) ←

Calculators’ Out Chaps ?

→→→ ( R1 + Rn ) is 0.3Ω when measured at ambient temperature ( say 20º C ) ←←← Ops “

 

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Evaluation of Voltage Drop Using Calculations : 2392-10 / 2391-20

( 612.14 ) Work Example , ( 2 )

The calculation method in regulation ( 612.14 ) as an example . ii to use diagrams or graphs showing maximum cable length
Versus load current for different conductor sizes with different percentage voltage drops for specific nominal voltages ,
Conductor temperatures and wiring systems

In the absence of such diagrams or charts , the voltage drop for a circuit may be calculated by using the tabulated values of voltage drop given in Appendix 4 of BS-7671 , in accordance with the instructions given in item 6 of that appendix , to do this , it will be necessary to ascertaining the type and size of cable by inspection , and to estimate the length of run for the circuit .

Insulation Résistance : ( New Installation Only ) This is Based on No-Power in the Building Yet :

Main Switch and all RCDs & MCBs are OFF ( Dead Test )
Inspection & Testing : 2392-10
61 : shall be applied when Verifying Insulation Resistance between non-earthed protective conductors’ and Earth

Where Surge protective devices ( SPD ) or other equipment are likely to influence the verification test , or be damaged , ←
( SPD ) – 250v dc . > 0.5MΩ

→ This is What Would Happen if there was a ( SPD ) fitting Over looked on a Circuit , ≈ ≈ ≈ ≈
Instrument 0n 500 dc / 0.1 MΩ ←←

Instrument 0n 500 dc / 0.1 MΩ
Lead on Neutral / Line Reading - 0.71MΩ , Which is a Fail
This is typical of Devices in the Circuit Effecting the Reading
You will have to go through Each Circuits Individual till you find the Fault ,
Once you find the ( SPD ) Fault Isolate the Circuit : MCB is switch off .
Re-do the Test with 500v dc your Readings are 99.9MΩ you have an a settable Value

Minimum Values of Insulation Resistance Listed in the Wiring Regs , ( 1MΩ is just an Exam Question ) in reality if I was getting readings any way near that Low on a New Installation
I would be doing further Investigations ,

SELV / PELV . Tables 61 ( Could be Lighting in the Bathroom 12Volts )
If the Circuit is ( SELV / PELV ) if it have equipment wired in ( SELV / PELV ) Test Voltage can be 250 V dc
Minimum Insulation Résistance ≥ 0.5MΩ

Remember that : Any Circuits Protected by RCBO will need to have RCBO Aux Tail Removed for Testing ← ←
RCBO Aux Tail must be Re-Connected after Testing

( 612.3.3 )
Where the circuit includes Electronic Devices which are likely to influence the results or be damaged .
Only a Measurement between the Live Conductors Connected together and the Earthing arrangement shall be made ,

Description of test RE- 2391-10

Performing this test is to ensure that there is continuity throughout the circuit, that there are no breakages and conductors have been connected correctly. Be sure you have isolated the supply before beginning the test.

Methods
Test method 1 : Short lead Test
Test method 2 : Long lead Test

Test Equipment
Low Ohm Resistance Meter

Note: R1 = Resistance of Line conductor, R2 = Resistance of CPC, Rn = Resistance of Neutral

Test Method 1: Short Lead Test
A Typical example would be to cross connect the Line and CPC conductors at the distribution board of the circuit going to be tested. At each point of the circuit, at test between Line & CPC should be performed. Noting that as you perform the tests further away from the cross connected ends at the distribution board, the higher the reading will become. The result recording the highest reading will be the R1 + R2 value on the test sheets. Make sure the test leads have been nulled on the tester or subtracted from the results accordingly

Test Method 2: Long Lead Test
This test is slightly different to method 1, as you are only testing the CPC. It is known as a long lead test because you may have to use an extra long cable to reach both ends of the CPC. ( Twin & earth can be used to create an extra long test lead). Making sure you null out the test leads before the test.
So basically what you have is your test meter connected to the Cpc at the distribution board and the other (extra long test lead, if necessary) test lead connected to the other end of the circuit. Perform the test, and record the highest result as the R2 value.

Sample Questions – 2392-10
Fundamental Inspection , Testing & Initial Verification – paper ( 3 )

1-C , 2-D , 3-B , 4-A , 5-A , 6-B , 7-A , 8-C , 9-D , 10-C , 11-A , 12-D , 13-C , 14-D , 15-D , 16-C , 17-D , 18-A ,
19-D , 20-A , 21-B , 22-A , 23-C , 24-B , 25-C , 26-A , 27-C , 28-A , 29-B , 30-D ,

Your Score should be 30 out of 30 :

Important Changes to Terminology and Definitions with the 17th Edition : 2392-10 / 2391-10

Among the changes to the scope and fundamental principles of the regulations is the inclusion of four new regulations for the protection of persons and livestock against voltage disturbances and electromagnetic influences.
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 and 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.

 

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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).
Several associations and trade bodies allow the issuing of a Minor Works Certificate.
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.
In a practical sense, for most electrical contractors involved in installation testing, the most frustrating part of the job is the recording of test data onto test certificates.
Invariably, current working practices involve the printing out or copying of a certificate for all premises to be tested at the beginning of the working day.
As circuit testing is undertaken on site the electrician will then usually record details of the inspection with written information on the 'dummy' certificate.
At the end of the day, back in the office, the manually recorded results will then be transferred to an 'original' certificate for the customer.

When Must The Tests Be Carried Out ? IEC ←← Our Cousins Over the Seas Regulations’ 2392-10 / 2391-10

The International Standard IEC-603664-6 Provides Requirements for “ Initial Verification “ and “ Periodic Verification “
Of an Electrical Installation :

“ Initial Verification “ Consists of Visual Inspection & Testing , of an Electrical Installation to Determine , as far as Reasonably Practicable , whether the Requirements’ of the Other Parts of IEC-60364 have been Met , Including Requirements for the Reporting of the Testing Results ,
The Initial Verification takes Place Upon Completion of a New Installation or Completion of Additions or of Alterations to Existing Installations ,

Periodic Verification : Provides the Frequency and the Requirements’ for Periodic Verification of an Electrical Installation to Determine ,
As far as Reasonably Practicable , Whether the Installation and all its Constituent Equipments are in a Satisfactory Condition for Use ,
Including Requirements for the Reporting of the Testing Results , Chapter 7 of this Guide Reports some Consideration of Periodic Inspection ,

This Guide will Not-Consider Visual Inspections ( for example the Checking of the Method of Protection Against the Electric Shock like Barriers
And Distances , Colour and Size of the Conductors , Presence of the Diagrams , Appropriate Selection of Materials , etc . )
But will Focus on the Various Testing Regimes and the Stipulated Values which these Tests should Deliver ,

Requirements For Testing An Electrical Installation :

The Following Tests shall be Carried Out where Relevant and should Preferably be Made in the Following Sequence :

* Continuity of the Protective Conductors and of the Main and Supplementary Equipotential Bonding Conductors :
* Insulation Résistance of the Electrical Installation :
* Protection by SELV & PELV or by Electrical Separation :
* Insulation Résistance of Non-Conducting Floors and Walls :
* Verification of Conditions for Protection by Automatic Disconnection of the Supply -
( Fault Loop Impedance , Earth Résistance , RCD Tests )
* Polarity and Phase Sequence Tests :
* Functional and Operational Tests :
* Voltage Drop :

The International Standard IEC-60364-6 Requires that all Measuring Instruments and Monitoring Equipment Used for the above Tests Comply with the Series IEC/EN 61557 , if Other Testing Equipment is Used , it shall Provide the Same Degree of Performance and Safety as a Minimum ,

Electrical Systems : “ Experiment “

An Electrical System Consists of a Single Source of Electrical Energy and an Installation ,
Depending on the Relationship between the Source and the Exposed ( Conductive ) Part of the Installation to Earthing ,
The Standards define the Type of System as Follows :

TT , System : the Accessible Conductive Parts are Earthed Indepently of the Source Earth :

TT : L1 ─────────────── ------- ────────────────────
……. L2 ─────────────── ------- ────────────────────
……. L3 ── * ──────────── ------- ───*──────────────── ( Single Phase )
…….. N ── * ──────────── ------- ───*──────────────── ( PE ) – ( R ) – Earthing

Earthing Rod ,

IT – System : the Live Parts are Insulated from the Earth ( or Connected to Earth Through an Impedance Z )
The Accessible Conductive Parts are Earth Independently :

……………………………………. 3-Phase
IT : L1 … . ────────────────── -------- ────────────────
……. L2 … . ────────────────── -------────────────────
……. L3 … * ────────────────── ------- ──*────────── L3 - ( Single Phase
…….. N * ─↓──────────────── ------- ─────*─────── ( PE ) – R ( Earthing
.. ……………..... Z
Earthing

IEC ←← Our Cousins Over the Seas Regulations’ 2392-10 / 2391-10

Insulation Résistance of the Electrical Installation :

The Insulation Résistance shall be Measured between each Live Conductor and the Protective Conductor or Earth ,
In Locations Exposed to Fire Hazards , a Measurement of the Insulation Résistance between the Live Conductors’ shall be Taken
The Insulation Résistance , Measured with the Test Voltage Values Indicated in the Table below are Satisfactory if each Circuit , with the Appliances Disconnected , has an Insulation Résistance Not-Less than the Appropriate Value given in the same table ,

Nominal Circuit ………………………….. Test Voltage …………………………… Insulation Résistance
Voltage ………………………………………. d.c. ………………………………….
────────────────────────────────────────────────────────────────
SELV , PELV ………………………………… 250 v ……………………………………… ≥ 0.5MΩ
( ≤ 50 v a.c. ≤ 120 v d.c. )
────────────────────────────────────────────────────────────────
Up to & including 500 v ……………………… 500 v ……………………………………... ≥ 1 MΩ
( including FELV )
────────────────────────────────────────────────────────────────
Above 500 v …………………………………… 1000 v …………………………………….≥ 1 MΩ
────────────────────────────────────────────────────────────────

Typically for 230 / 400 v Circuits ( Excluding SELV & PELV ) IEC 60364-6 Requires that the Insulation Résistance at a Test
Voltage of 500 v d.c. shall be 1MΩ as a Minimum :

NOTE: Where Surge Protective Devices ( SPDs ) are Likely to Influence the Test or be Damaged ,
Such Equipment shall be Disconnected before Carrying Out the Insulation Résistance Test , Where it is Not Reasonably Practicable to Disconnect such Equipment ( e.g. in Case of Fixed Sockets-Outlets Incorporating an ( SPD ) the test Voltage for the Particular Circuit may be Reduced to 250 v d.c. , but the Insulation Résistance must have a Value of at Least 1MΩ

Protection by SELV , PELV or by Electrical Separation : 2392-10 / 2391-10

Even if the Automatic Disconnection of Supply by Circuits-Breakers , Fuses and RCDs , is Normally the most Common Protection Method . there are Other Protection Methods like Protection by SELV , PELV or be Electrical Separation or by Non-Conducting Floors and Walls ,

Only for these Cases shall the Separation of Live Parts from those of Other Circuits , be Confirmed by a Measurement of the Insulation Résistance , The Résistance Values Obtained must be in Accordance with table :
Below there is an Example of the Measured of Insulation Résistance to Confirm the Separation of Live Parts from those of Other Circuits :

Test Instrument : (1) One Lead On ( Between the Output of the Transformer ) 2-Wires
Test Instrument : (2) One Lead On ( And the Other Live-Parts – for SELV / PELV )
( And the Equipotential Bonding Rads ( SELV Only )

Insulation Résistance of Non-Conducting Floors and Walls :

When it is Necessary to Comply with the Requirements of the Protection by Non-Conducting Locations , the Floor and Wall Insulation Résistance / Impedance shall be Tested
In Part 6 of IEC 60364 Methods for Measuring the Insulation Résistance / Impedance of Floors and Walls are given as Example ,

IEC ←← Our Cousins Over the Seas Regulations’ 2392-10 / 2391-10

Verification of Conditions for Protection by Automatic Disconnection of the Supply :

Automatic Disconnection of the Supply is Required where a Risk of Harmful Pathophysiological Effects to a Person may arise due to a Fault as a Result of the Value and Duration of the Touch Voltage ,
The Verification of the Efficacy of the Measures for Protection against Indirect Contact by Automatic Disconnection of Supply is Treated below :

In Case of TN-systems :

According to the International Standard IEC 603664 , for TN- system the Characteristics of the Protective Device and the Circuit Impedance shall fulfil the following Requirements :
( Zs x Ia ≤ Uo )
Zs : is the Fault Loop Impedance in Ohms ,
Uo is the Nominal Voltage between Phase to Earth ( Typically 230 V AC for Single Phase & Three Phase Circuits ,
Ia is the Current Causing the Automatic Disconnection of the Protective Device within the Maximum Disconnecting Times Required by IEC 60364-41 that are :

- 400 ms for Final Circuits Not Exceeding 32A ( at 230 / 400V ac )
- 5s for Distribution Circuits and Circuits Over 32A ( at 230V / 400V ac )

The Compliance with the above rules shall be Verified by :
(1) Measurement of the Fault Loop Impedance ( Zs ) by Loop Tester :
(2) Verification of the Characteristics and / or the Effectiveness of the Associated Protective Device , This Verification shall be Made :

 

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- for Circuit-Breakers and Fuses , by Visual Inspection ( i.e. Short Time or Instantaneous Tripping Setting for Circuit-Breakers ,
Current Rating and Type for Fuses )
- for RCDs , by Visual Inspection and Test using RCD Testers Recommending that the Disconnecting times mentioned above are met ,

For Instance in a TN-system with nominal mains Voltage Uo = 230 V Protected by General Purpose gG fuses or MCBs ( Miniature Current Breakers ) required by IEC 898/ EN 60898 , the ( Ia ) and Max ( Zs ) Values could be :

Protection by ( gG fuses )
With Uo of 230 V
Rating ( A ) ……. Disconnection …………. Disconnection ( Regs BS – table 41.4
………………….. time 5s ………………….. tine 4s
……………….. Ia … Zs …………………. Ia … Zs ……
……………….. (A) .. (Ω) …………………(A) .. (Ω) …..
6 ……………… 17 ... 13.5 ……………….. 38 … 8.52 ….
10 ……………...31 ... 7.42 ……………….45 .. .5.11 ….
16 ……………...55 ... 4.18 ………………..85 … 2.7 ….
20 ……………...79 ... 2.91 ………………..130 …1.77 ….
25 ……………..100 ... 2.30 ……………….160 …1.44 ….
32 ……………..125 ... 1.84 ……………….221 …1.04 ….
40 ……………..170 ... 1.35 ………………. --- ….. ---
50 ……………..221 ... 1.04 ………………. --- ….. ---
63 ……………..280 ... 0.82 ………………. --- ….. ---
80 ……………..403 ... 0.57 ………………. --- ….. ---
100 ……………548 ... 0.42 ………………. --- ….. ---

The most Complete Loop Testers or Multifunction Testers also have the Prospective Fault Current Measurement , in this case Prospective Fault Current Measured with Instruments must be Higher than the Tabulated ( Ia ) of the Protective Device Concerned ,

Below is a Practical Example of Verification of the Protection by MCB in a TN-system ,
According to the International Standard IEC 60364 ,

Max Value of ( Zs ) for this Example is 1.44Ω ( MCB / 16A ) Characteristic C , THE Instrument reads 1.14Ω ( or 202A on Fault Current Range ) it means that the Condition ( Zs x Ia x ≤ Uo is Respected ,
In fact the ( Zs of 1,14Ω is Less than 1.44Ω ( or the Fault Current of 202A is more than ( Ia ) of 160A .
In Other words , in case of Fault between Phase & Earth , the Wall Socket Tested in this Example is Protected because the MCB will Trip within the Disconnection time Required ,

L3 -
N -
PE -

17th Edition - & -
Chapter 41 :
Protective Measure Against Electric Shock :

Under Some Sub-Cat ; ( Basic Protection ) ( Fault Protection ) ( Additional Protection )
Part-4 Protection for Safety

411.2 Requirements for Basic Protection :
411.3 Requirements for Fault Protection :
411.3.3 Additional Protection :

Now Designated ↔ Basic Protection , ( 410 ) ( i ) “ Insulation “ Applied to Live Parts “ Preventing Touching Live Conductors , Protection against Electric shock under fault-free conditions .

Note : for Low-Voltage Installations , systems and Equipment , Basic Protection generally corresponds to Protection against Direct Contact ,
That is “ Contact of Persons or Livestock with Live-Parts :

Now Designated ↔ Fault Protection ( 410 ) ( ii ) “ Protective Earthing “ Automatic Disconnection of Supply , ( ADS ) ←
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 ,
Is “ Contact of Persons or Livestock with → Exposed-Conductive-Parts which have become Live Under Fault Conditions ← :

415 : Additional Protection : Is Not Defined in Part 2 of the Regs , it is Detailed in Section ( 415 ) ←

Additional Protection against Electric shock can be Provided by Either !
( 415.2 ) Supplementary Equipotential Bonding ,
( 415.1 ) Additional Protection : Residual Current Devices ( RCDs ) Not Exceeding 30mA ↔ Operating time Not Exceeding 40mS

Protective Measures Against Electric Shock ,

* ( Basic and Fault Protection )
Extra Low-Voltage : SELV / PELV
SELV , is a Safety Isolation Transformer ( No Earth Provisions on the Secondary Side of the Transformer ) 230V- P │ ↔ │S- 12V a.c.
PELV , The Earth Provisions Continues through to the Load Side :

When it comes to Inspection there’s several things your got to check ? the First of those is does the Location your in which in this Location is the Bathroom has Requirements for SELV or PELV ,

Part 7 :Special Installation or Locations

You Need to Look up : P-169 / fig 701.2

( 701.55 ) In a Room Containing a Bath or Shower ; Suitable Fixed Current-Using Equipment , ( in Zone 0 , SELV / Remember Not PELV ,
Remember SELV is Located Outside the Zones ,
( iii ) SELV at a Nominal Voltage Not Exceeding 12V ac rms or 30V ripple-free d.c.

Zone O , Area Within the Bath or Shower : ▪▪▪
Zone 1 , Area Directly above Barth or Shower : ( Up to 2.25m Above the Finished Floor ▪▪▪
Zone 2 = Defined as Area Within 0.60m Circumference from the Bath or Shower : ▪▪▪

Regs : 17th , Socket-Outlet are Prohibited within a Distance of ( 3 m ) Horizontally from the Boundary of Zone 1 , This One will Come Up : p–167 ▪▪▪
Or ( FSU ) for Electric Towel Rail : ( RCD / Spur 30mA )

Arm’s Reach : N/A Accessibility in Zone O / Zone 1
N/A Electrical Equipment in Bathroom , ↔ 1 or more ( RCD 30mA “ Including Lighting Circuits “ ▪▪▪
( 701.512.2 ) IPX7 (i) Zone O / IPX4 , (ii) Zone 1 / 2 ( Lighting Bathroom ) ▪▪▪

( 702.522.24 ) Junction boxes : This One will Come Up : p–167 ▪▪▪▪
A Junction box shall Not be Installed in Zone 0 or 1 but in the case of SELV Circuits it is Permitted to Install Junction boxes in Zone 1

Termed an “ Extraneous Conductive Part “ Water Pipe , ( Not Part of an Electrical System / Equipment )

Functional Extra-Low Voltage ( FELV ) Exposed Conductive Parts of an FELV System are Connected to the Protective Conductor of the Primary Circuit of its Source : ( 411.7 )
Following shall be Used as Source of FELV , Transformer with Separations’ between Windings’ :

Heath and Safety 2392-10

The Electricity at Work Regulations 1989

12 Means for Cutting off the Supply and for Isolation ,
13 Precautions for work on Equipment made Dead ,
14 Work on or near live Conductors ,

12 Means for Cutting off the Supply and for Isolation

12.- (1) Subject to paragraph (3), where necessary to prevent danger , suitable means
( including , where appropriate , methods of identifying circuits ) shall be available for-
(a) cutting off the Supply of Electrical energy to any Electrical equipment ; and
(b) the isolation of any Electrical equipment .
(2) In paragraph (1),” isolation “ means the disconnection and separation of the
electrical equipment from every source of electrical energy in such a way that this
disconnection and separation is secure .
(3) Paragraph (1) shall not apply to electrical equipment which is itself a source of
electrical energy but, in such a case as is necessary , precautions shall be taken to prevent ,
so far as is reasonably practicable , danger .

Electrical Test Equipment for use by Electricians ( GS-38

Guidance on Safe Isolation Procedures for Low Voltage Installations :

Domestic : the Fundamental Principle of Safe Isolation Practice is that the Point of Isolation should always be under the Control of the Person who is carrying out the work at all Times : ( Locking Off )

For work on LV Electrical Equipment or Circuits , it is Important to Ensure that the Correct Point of Isolation is Identified ,
An Appropriate Means of Isolation is Used , and the Supply Cannot Inadvertently be Reinstated while the work is in Progress ,

Warning / Caution Notices should also be Applied at the Point(S) OFF Isolation , and the Conductors must be Proved to be Dead
At the Point of “ Work “ before they are Touched ,

Firstly you Must Guarantee the Point of Isolation is Correct , that the Circuit that your need to working on , making Sure that Correct Identification was Carried Out : ↔ “ Never Take for Granted “ ↔ the Circuit Chart or Identification of the Device :

( Isolation of Individual Circuits Protected by Circuit-Breakers )
Where Circuit-Breakers are Used , the Relevant Device should be Locked-Off Using an Appropriate Locking-Off Device
With a Padlock which can Only be Opened by a Unique Key or Combination , The Key or Combination should be Retained by the Person Carrying Out the Work .

The Principle is that Each Person carrying out such work should have Control of their own Point(s) of Isolation and Not Rely
On Others to Prevent Deliberate or Inadvertent Energization ,

( Typical Devices for Proving Dead ) “ Remember “ 2392-10 you’ll be Asked some of these Q/A “

The Procedure for Proving Dead should be by Use of a “ Proprietary Test Lamp or Two-Pole Voltage Detector as Recommended
In Guidance Note GS-38 ,
Electrical Test Equipment for Use by Electricians , Non-Contact Voltage Indicators ( Voltage Sticks ) and Multimeters should Not be Used ,

The Test Instrument should be Proved to be Working on a Known Live Source or “ Proprietary Proving Unit , before and after Use ,
All Conductors of the Circuit , Including the Neutral , should be Tested and Proved Dead :

 

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Domestic Electrician : 2392-10

Note : in TT Systems , the Incoming Neutral Conductor Cannot Reliably be Regarded as being at “ Earth Potential :
This Means that for TT Supplies , a Multi- Pole Switching Device which Disconnects the Phase-Neutral Conductors
Must be Used as the Means of Isolation .

Note : in IT Systems , All Poles of the Supply Must be Disconnected , in these Circumstances , Single-Pole Isolation ,
Such as by Fuses or Single-Pole Circuit-Breakers , “ is Not Acceptable “

Temporary Disconnection of Incoming Supply :

For Some Type of Work on Existing Installations , such as the Replacement of Main Switchgear , Consumer Units etc .
It is necessary for the Distributors Service Fuse(s) to be withdrawn in order to Disconnect the Incoming Supply for
The Purpose of Isolation ,

Legally , Service Fuses can be Withdrawn Only by the Distributor , or by those they have Expressly Authorized to Carry Out such Work ,

Note : Some DBs are Manufactured with “ SLIDER SWITCHES “ to Disconnect the Circuit from the Live Side of the Circuit-Breaker
These Devices should “ NOT “ be Used as a Means of Isolation for Circuits , as they “ DO NOT “ meet The Requirements for Isolation
And the “ Wrong Switch “ Could Easily be Operated on Completion of the Work :

Domestic Electrician : 2392-10
Additional Precautions :

New Installations ,

New Installations can be a Particular Hazard as some of the Circuits or Equipment may require to be Modified after the
Installation has been Energized ,
It is therefore Important that every Protective Device is Correctly Identified at each Distribution Board before any Energizing takes place ,
And Safe Isolation Procedures , such as Locking-Off Circuit-Breakers as Particularly where a Number of Electricians are working on the same Installation ,

Alterations & Additions :

Alterations & Additions to Existing Installations can also be Particularly Hazardous , Records including Circuit Identification may not be Available ,
Or may be Inadequate or Incorrect , it is therefore Particularly Important to ensure that Circuits to be worked on has been Correctly Identified for Isolation Purposes ,

Neutral Conductors :

Care should be taken when working on Neutral Conductors of Circuits , The Practice of “ Borrowing Neutral , ( 314.4 ) i.e. making
Use of the Neutral of one of the Circuit for use on another Circuit , is Not Permitted by BS-7671 , this Dangerous Practice , however , may still be Encountered ,
Lighting & Control Circuits’ are the most Common Example : where this Practice is found , in these Circumstances , the Neutral
Conductor can become Live when the Conductor is Disconnected , if a Load is Connected to that Circuit ,
It is also Difficult to Identify Specific Neutral Conductor in “ Bunches “ of Single-Core Cables , such as where Enclosed in Trunking or Conduit ,
And care should be taken when severing such Cables that the correct Conductor has been Identified ,

Guide To Isolation Procedure : GS-38 / 2392-10 ( this will cover your Butt )

Pocket Size Guide ,

Step (1) : ( Locked Off )
Check it is Safe and Acceptable ( with the Occupier / User ) to Isolate, if the Isolator is an Off-Load Device ,
Remove the Load . Open the Means of Isolation for the Circuit(s) to be Isolated and Secure the Isolating Device in the Open Position with a
Lock or Other Suitable Means :

Step (2) : ( Proving Unit )
Prove the Correct Operation of a Suitable Voltage Detection Instrument , See Note (v) Guidance on Voltage Detection Instruments is given in
HSE Guidance Note GS-38 – Electrical Test Equipment for use by Electricians : against source ,

Step (3)
Using a Voltage Detection Instrument , Check that there is No Dangerous Voltage Present on any Circuit Conductor to be
Worked on , it is Important to Confirm that Conductors’ are Not Energized , Example ; due to a Wiring Fault , Check Terminal
Voltage between : (1) - ( Earth & Phase ) (2) – ( Neutral & Phase ) (3) – ( Earth & Neutral ) ,

Notes :
(a) in practice the equipment being worked on is likely to be remote from the consumer unit , example ,
A socket-outlet located remotely from the means of isolation , in this case it is necessary to check
that all the sockets-outlet contact terminals are “ Dead “
(b) when checking for a voltage between an earth terminal and live ( including neutral ) terminals ,
The test probe should make contact with the earth terminal first , to reduce the risk of the remaining
Probe becoming live ,

Step (4)
Prove the voltage detection instrument again against the known source to check that it was functioning correctly
When the circuit(s) were tested for the presence of voltage .

Notes :
(1) The Electricity at Work Regulations 1989 , require precautions to be taken against the risk of death or personal injury
from Electricity at Work activities Regulations ( 12 ) requires that , where necessary to prevent Danger : a suitable means is
available for cutting off the supply of Electrical Energy to any Electrical Equipment ,

Proving Dead Isolated Equipment or Circuits :

It is Important to ensure that the correct point of Isolation is Identified before Proving Dead ,
Following Isolation of Equipment or Circuits and before starting work it should be proved that the Parts to be worked on and those nearby , are Dead , it should never be Assumed that Equipment is Dead because a Particular Isolation Device has been Placed in the OFF Position ,

 

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In the Case TT Systems : 2392-10 ( this will come up on the 17th Edition , -&- )

According to the International Standard IEC 60364 , for TT Systems the Characteristic’s of the Protective Device and the Circuit Resistance shall fulfil the following Requirements : ( Ra x Ia ≤ 50V )
Where :
( Ra ) is the Sum of the Resistance in Ω of the local Earth System and the Protective Conductor for the Exposed Conductive Parts ,
( 50 ) is the Maximum Safety Touch Voltage Limit ( It can be 25v in Particular Cases like Construction Sites , Agricultural Premises , etc . )
( Ia ) is the Current Causing the Automatic Disconnection of the Protective Device within the Maximum Disconnecting Times Required IEC 60364-41 :
-- 200mS for Final Circuits Not Exceeding 32A ( at 230 / 400 AC )
-- 1000mS for Distribution Circuits & Circuits over 32A ( at 230 / 400 AC )

The Compliance with the above rules shall be Verified by :
(1) Measurement of the Résistance ( Ra ) Regs : BS – 411.5.3. ↔ of the local Earth System by Loop Tester or Earth Tester .
(2) Verification of the Characteristics’ and / or the Effectiveness of the RCD Associated Protective Device ,

Generally in TT Systems , RCDs shall be Used as Protective Device and in this Case , ( Ia ) is Rated Residual Operating Current ( I∆n ) ,
For Instance in a TT System Protected by a RCD the Max ( Ra ) Values are :

Rated Residual Operating :
………Current ………………….. 30 ----- 100 ----- 300 ----- 500 ----- 1000 ----- mA
………. ( Ra )
( with touch voltage of 50V ) … 1667 ----- 500 ----- 167 ----- 100 ----- 50 ----- Ω
………. ( Ra )
( with touch voltage of 25V ) … 833 ----- 250 ----- 83 ----- 50 ----- 25 ----- Ω

Practical Example of Verification of the Protection by RCD in a TT System According to the International Standard IEC 60364 ,

The Standard Describes two methods for Testing the Résistance ( Ra )

- Volt-Ampere Method , Using Classical Earth Résistance Testers or the most Complete Multifunction Testers by sticking Two Auxiliary Earth Electrodes into the Ground . ( R – PE ) ( RCD 30 mA )

Fault Loop Impedance Method ( Loop Tester ) Regs BS- 6132.9 : the IEC 60364-6 Describes a Safe and easy Method to Test Earth Résistance
Where in a TT System , the Location of the Installation ( e.g. in Towns ) does Not Practice allow the two Auxiliary Earth Spikes to be Inserted into the Ground ,
This Method consists of the Measurement of the Fault Loop Impedance with a Loop Tester or a Multifunction Tester , in a TT Systems
Will in Practice give the Earth Résistance , ( RCD 30 mA )

For these Example the Max Permissible Value is 1667Ω ( RCD = 30mA and Contact Voltage Limit of 50V )
The Instruments’ Reads 12.74Ω : thus the Condition ( Ra ≤ 50 / Ia ) is Respected , However , considering that the RCD is Essential for Protection , it must be Tested as Follows :

Operation of Residual Current Devices ( RCDs ) in TT System :
Given that when the Protective Device is an RCD , ( Ia ) is Typically ( 5 ) times the rated Residual Operating Current ( I∆n ) then the RCD must be Tested Using RCD Testers or Multifunction Testers Recommending that the Disconnecting Times Required in IEC 60364-41 are Confirmed ,

The RCD Testers or Multifunction Testers can Perform the Tests for Single-Phase and Three-Phase RCDs by Measuring the Tripping Time , in TT System at 230 / 400V , the Tripping Time Measured by an RCD Tester or a Multifunction Tester shall be Lower than the Maximum Disconnecting Times as Defined by IEC 60364-41 that are :

- 200 mS for Final Circuits Not Exceeding 32A :
- 1000 mS for Distribution Circuits & Circuits Over 32A :

It is also Good Practice to Consider even more Stringent Trip Time Limits , by Following Standard Values of Trip Times at ( I∆n ) Defined by IEC 61009 ( EN 61009 ) and IEC 1008 ( EN 61008 ) These Trip Time Limits are listed in the Table Below :

Type of RCD …………………………………… Test at I∆n
General ( G) …………………………… 300mS Max . allowed value :
────────────────────────────────────────── ( Regs , BS – p-243 ,
General ( S ) …………………………… 500mS Max . allowed value :
………………………………………….. 130mS Min . allowed value :

Note : These Tripping Time Values are Applicable to RCDs Correctly Installed According to the Manufacturer Specifications :

( Old ) General Purpose RCDs to BS-4293 : Operating time less than 200mS : Remember ↔ ↔ ( BS- )
RCDs to BS-EN 61008 & BS-EN 61009 , Operating time below 300mS : Remember ↔ ↔ ( BS-EN )

Remember ↔ ↔ Note 2 Where ( Ra ) is Not known , it May be Replaced by ( Zs ) Regs : 411.5.3 )
411.5.3 ) (ii) Ra x I∆n ≤ 50V , ( Ze = Ra , electrode : Max permitted is 1666Ω , based on Not allowing the Voltage to Rise above ( 50V )

For IT Systems : IEC ←← Our Cousins Over the Seas Regulations’ 2392-10 / 2391-10

Compliance with the rules of IEC 60364-4-41 shall be Verified by Calculation or Measurement of the Current in case of a first Fault at the Line Conductor or at the Neutral :
Where similar conditions to TT or TN- Systems Occur , in the event of a second Fault in another Circuit , Verification is made as for TT or TN- systems as described above ,

Note : During the Measurement of the Fault Loop Impedance , it is necessary to establish a connection of negligible Impedance between Neutral Point of the System and the Protective Conductor Preferably at the Origin of the Installation or ,
Where this is Not Acceptable , at this Point of Measurement ,

Measurement of the Earth Electrode Résistance :
The International Standard IEC 60364-6 Provides Information Regarding the Measurement of the Résistance of an Earth Electrode for TT, TN and IT Systems , this Measurement shall be made by the Volt-Amperometric Method Using Two Auxiliary Earth Electrodes ,
The Instrument that covers , this Requirement is the Earth Tester : ( Measurement of the Earth Electrode Résistance )

( Earth Electrode , under Test ) 3 – Leads Used , 0ne on Earth Electrode
( Auxiliary Earth Electrodes , ) 0ne on each Aux Electrode ,

Note : The Auxiliary Earth Electrodes must be Placed at Sufficient Distance from the Earth Electrode Under Test in Order to
Avoid Overlapping of the Résistance Areas of the Electrodes ,

Polarity & Phase Sequence Tests :

Where the Standard Prohibits the Use of Single-Pole Switching Devices for the Neutral Conductor ,
A Test shall be made to Verify that all such Devices are Used Only for Line Conductor(s) ,
Where the Rules Require Double Pole-Switches , a Test shall be made to Verify that the Poles of such Devices are Connected
Correctly to the Appropriate Conductor ,

In the case of Multiphase Circuits it shall be Verified that the Phase Sequence is Maintained ,
In Particular a Test shall be made to Verify that the Devices ( i.e. Motors ) are Connected in the Correct Phase Sequence by a Phase Rotation Tester ,
Two Example : a Polarity Test Determine the Phase Conductor Using Digital Multimeter as a Voltmeter ,
( “ DEAD TEST “ Multimeter : One Lead on Phase Conductor / Other Lead on Earth Terminal : ( PE )
( Motor 3-Phase ) 3 – Leads , 1 / L1 , 1 / L2 , 1 / L3 , ( Remember Contacts are Open ,

Functional Tests :

Assemblies , such as Switchgear and Control gear Assemblies , Drives , Controls , and Interlocks , shall be Subjected to a Functional Test to Show that they are Properly Mounted , Adjusted and Installed in Accordance with the relevant Requirements of the IEC 603664 , Protective Devices shall be Submitted to Functional Tests , if Necessary , in Order to Check if they are Properly Installed and Adjusted ,

The fundamental rule of protection against electric shock, according to IEC 61140, is that
hazardous-live-parts must not be accessible and accessible conductive parts must not be
hazardous live, neither under normal conditions nor under single fault conditions.

 

[castlon11]

“ Rcd's “


Surface run cables do not require RCD protection. OSG p22

This statment conflict's with so many other regulations when taken out of context.

Other than this, very nice post, thanks