Re-take - Useful Information for 2394 :

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Scenario . (( One way of looking at it ))

Neutral / Earth fault can remain undetected . they do exist

Ohms law . Scenario .
The résistance of the Earth-path : " room for thought " TT system with an earth-rod résistance of ( 100Ω )

( PD , potential-difference ) neutral and Earth .. 30mA to flow to Earth will require a voltage-difference between the neutral-conductor and Earth of ,
3 - volts .. ( 0.03 x 100 ) = 3V .

The resultant ( PD ) between neutral and Earth may be sufficient to cause the current to flow in the circuit-protective-conductor , Hence .
the nature of the fault is ( Load-dependent ) This may cause the RCD to trip randomly at times and the fault may be described as ;

The Pursuit of making (( Unwanted tripping )

 

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Faults are not always just a single problem & one fault can hide or affect another.

 

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" Alternating current " its about potential difference ... ( ~ ) in and out .

Current should flow from Line to Neutral . ( a.c ) it will reverse direction 50 times a second, but convention says it flows from Line to Neutral .

BS-7671:2011: tell us of , Types of system earthing . Three-systems . TN-S , TN-C-S ( PME ) , TT - system .

TN-C-S ( PME ) Fig 3.9

Standard - reminds us , RCDs monitors only .

Neutral to Earth faults ..
i) This depends on two-factors .. ( The PD ) potential difference between the neutral conductor & Earth .
ii) The résistance of the earth-path .

Significant neutral to Earth résistance can also exist ; Therefore , TT - , TN-S , can remain undetected . ( IR ) insulation resistance test . C&Gs

TN-C-S ( PME ) .. ( PD ) Neutral & Earth .
if the RCD is to trip due to a Neutral & Earth fault , the ( PD ) between the neutral-conductor and Earth must be sufficient to cause at least some of the returning neutral current to return to the origin via the circuit-protective-conductor rather than via the ( Neutral-conductor )

TN-C-S ( PME ) .. The neutral conductor and Earth are likely to be ( Substantially the same potential ) due to the neutral / earth link in the ( Cut-out ) in such a situation , no current will flow & the RCD will not trip . However .

When the load of the circuit with the neutral / Earth fault is energised , the current flow causes a voltage drop in the neutral-conductor and this voltage drop results in a ( PD ) between it and Earth .

The greater the load , the greater the current flow and hence the greater will be the voltage drop . if the voltage drop is sufficient , some of the returning neutral-conductor will flow through the circuit-protective-conductor , should enough current flow through the circuit-protective-conductor , the RCDs search will " See an imbalance and cause the RCD to operate " Therefore , in a TN-C-S with no load or with a very light load . a neutral / Earth fault my remain undetected .

 

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Borrowed Neutral . is an infringed by this practice . ?? British ( Standards )

Situation where a Neutral is wired across two or becomes live once you switch the circuit off that you are working on, effectively reversing the live conductor 230V to the neutral part of the circuit you thought you had just isolated.

(( Borrowed Neutral )) it may already be a killer and not know it. ( it's still out there ) cleaning someone also mess .

Regulation 314.4. recap :
Where an installation comprises more than one circuit , each final circuit shall be connected to an separate way in a Distribution-board . Consumer-unit .

The wiring of each final circuit shall be electrically separate from that of every other final circuit . so as to prevent the indirect energizing of a final circuit intended to be isolated .

 

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Blast from the Past . Extracts

16th Edition ◄► . Isolating timer Fans ..

Does BS-7671 require items of electrical equipment to be isolated locally ?

The answer is that there is no specific requirement for equipment to be isolated locally. However, careful consideration must be given to the positioning of isolating devices.

While it is important that all the requirements of BS-7671: regarding isolation are adhered to, the following comments regarding the isolation of single-phase electrical equipment are offered for consideration:

Regulation 461-01-01 requires that each circuit must be capable of being isolated from each of the live supply conductors, except as required by Regulation 460-01-04, which states that, for TN-S or TN-C-S systems, the neutral conductor need not be isolated.

Regulation 537-02-02 permits the use of overcurrent protective devices, such as circuit-breakers to BS-EN-60898-1 and RCBOs to BS-EN-61009, to be used as isolators.

Remote isolation
Where isolation is remote, precautions must be taken to prevent equipment from being inadvertently or unintentionally energised (Regulations 461-01-01 and 476-02-02). This effectively means that overcurrent devices must be capable of being locked in the off position.

Where rewireable fuses to BS-3036 are used, the fuse controlling the circuit to be isolated could be removed and put in a safe place where it could not be replaced without the knowledge of the person working on the circuit.

This means of isolation would not be suitable for isolating a timer fan in a windowless room because, in isolating the fan, the lighting circuit which supplies it is also isolated

The artificial light in a windowless room has been switched off when work is to be carried out on the fan. A lead light could be used to provide light but this introduces a trip hazard. ( PS, buy a head torch .. LED )

Three-pole isolating switch is your ( Practical solution ) Safe isolation . in the case of timer fans in windowless room it is recommended in the interests of safety.

 

[Richard Burns]

For Amberleaf:
BS-7671:2008: Requirements for electrical installation(s) ... 542.4.

Main Earthing Terminal MET)

Disconnection of ..........

1 ) Means for disconnecting the earthing conductor

Regulation 542.4.2 of BS-7671 requires means for disconnection of the earthing conductor be provided at or near the Main Earthing Terminal (MET) of an installation. The purpose of the means of disconnection is to allow measurement of the external earth fault loop impedance ( Ze ) and, where the installation forms part of a TT system , measurement of the installation earth electrode résistance.

Regulation 542.4.2 is reproduced as follows for ease of reference

Regulation 542.4.2
‘ To facilitate measurement of the resistance of the earthing arrangements, means shall be provided in an accessible position for disconnecting the earthing conductor. Such means may conveniently be combined with the main earthing terminal or bar. Any joint shall be capable of disconnection only by means of a tool. ‘
As Regulation 542.4.2 does not stipulate a particular arrangement for the means of disconnection, any suitable arrangement may be used which meets all the requirements stated in the regulation. Examples of suitable arrangements are given in Figures 1 and 2.

Fig 1, shows an arrangement in which the earthing conductor is withdrawn from its terminal at the MET, by the use of a tool (a screwdriver), in order to facilitate the resistance measurement of the means of earthing, and then replaced and re-secured into the terminal after the measurement has been made. This arrangement is not suitable for situations where the end of the earthing conductor at the MET cannot be conveniently manoeuvred, such as within an enclosure in which there is insufficient room or where the diameter of the earthing conductor is too large to provide sufficient flexibility.

Fig 2 , shows an example of a MET incorporating a bolted link which is opened or removed by the use of a tool ( such as a spanner ) in order to disconnect the earthing conductor, and then reinstated and re-secured after the resistance measurement to the means of earthing has been carried out.

Whatever arrangement is provided as the means for disconnection of the earthing conductor, in addition to the requirements of Regulation 542.4.2 mentioned earlier, the requirements of the Electricity at Work Regulations and those of Section 522 of BS-7671 must be met.

Regulation 9 of the Electricity at Work Regulations requires that ‘ if a circuit conductor is connected to earth or to any other reference point, nothing which might reasonably be expected to give rise to danger by breaking the electrical continuity or introducing high impedance shall be placed in that conductor unless suitable precautions are taken to prevent that danger ’.

For example, where a joint or bolted link is provided, it must be arranged to ensure the integrity of the conductor. The connection or link must not be able to be removed in such a way as would give rise to danger. Ways of achieving this would normally include one or more of the following:

• Disconnection requires a deliberate act using a tool .... This is an explicit requirement of Regulation 542.4.2
• The joint or link should be accessible only when the installation is isolated
• The joint or link should be accessible to skilled persons only

• Section 522 of BS-7671 requires that the means for disconnection must be protected where necessary against external influences (such as vandalism, unauthorized interference, damp, corrosion, dust, vibration or mechanical impact).

Earthing conductor at the MET. Earthing conductor is withdrawn from its terminal for testing purposes. Withdrawal is a deliberate act involving the use of a tool.

Example of MET with disconnectable link

Testing : ( MET )
542.4.2. To facilitate measurement of the résistance of the earthing arrangements ,
Mean's ; shall be provided in an accessible position for disconnecting the ( Earthing-conductor ) Such means may conveniently be combined with the main-earthing-terminal or bar .

Any joint shall be capable of disconnection only by means of a tool .
Main Earthing Terminal : (MET)

1. The requirement to have a Main Earthing Terminal (MET)
Regulation 542.4.1 of BS-7671 requires a Main Earthing Terminal (MET) be provided for every installation.
The MET is required to connect the following to the earthing conductor of the installation, as illustrated in Fig 1 (Regulation 542.4.1 refers):

i) The circuit protective conductors
ii) The protective bonding conductors
iii) Functional earthing conductors (if required)
iv) Lightning protection system bonding conductor, if any (see Regulation 411.3.1.2).

MET connecting various conductors to the earthing conductor, as required by Regulation 542.4.1.

For practical reasons, the MET is normally situated at or near the origin of the installation (that is, the position where the electrical energy is delivered)

(Means of earthing) ....................... TN- TT systems

Example of the use of the earthing bar as a MET in an item of main switchgear

R/P 26
Distribution board :
An assembly containing switching or protective devices ( e.g. fuses , circuit-breakers , residual current operated devices ) associated with one or more outgoing circuits fed from one or more incoming circuits , together with terminals for the neutral and circuit-protective-conductors . refer

R/P 25
Consumer unit : .. ( CCU )
may also be known as a consumer control unit or electricity control unit . refer

Examples of brass terminal bars or blocks used as a MET


MET incorporating a bolted link to permit the disconnection of the earthing conductor for testing purposes

 

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Verification of earth fault loop impedance test - results .. ( Implications )

Verification : R/P 36
All measures by means of which compliance of the electrical-installation with the relevent requirements of BS-7671: are checked , comprising inspection , testing and certification .

612.1. recap
it is important to recognise that BS-7671: requires the inspector not only to test the installation but also to compare the results ;
with relevant design criteria ( or with criteria within BS-7671: )

On the question of danger from any test .. this must be assessed by the Inspector for the given situation .

Earth fault loop impedance testers . BS-EN-61557-3 . ( Part 3 )

( Earth-fault-loop ) in the eyes of C&Gs .. Verification
Reason : this instrument functions by creating , in effect an Earth-fault for a brief moment . Instrument should only allow an Earth-fault to exist for a maximum of ( 40mS )

4.5. GN-3 has advocated , This means that the instrument should cut off the test current after ( 40mS )

Connected to a circuit via , a Plug .. ( Circuit-loop ) 612.9. ( Zs )
By " flying leads " connected separately to Line , Neutral , Circuit-protective-conductor .

612.9. Where protective measures are used which require a knowledge of earth-fault-loop-impedance ... The relevant impedances shall be :
Measured

Reporting : R/P 33 . Communicating the results of periodic inspection and testing of an electrical installation to the person ordering the work .

Periodic testing : 3.10.
621.2. The periodic testing is supplementary to the inspection of the installation

3.8. Requirements for inspection & testing
The purpose of periodic inspection and testing is to provide an engineering view on whether or not the installation is in a satisfactory condition where it can continue to be used in a safe way .

if you have conducted the inspection & test of an installation thus far correctly , then you should have already carried out a form of polarity test .
You have done this using your senses during the inspection , prior to picking up an instrument .

re-cap Inspection: R/P 29 .
Examination of an electrical installation using All the senses as appropriate .

Polarity : 2 different scenarios ... ( Dead or Live testing ) that require a polarity test
- origin of the installation ... The polarity of the main-supply must be correct .
- distribution boards ... The polarity of the main-supply must be correct .
- accessible socket-outlets .
- extremity of radial circuits ... All polarities of socket outlet(s) must be verified

Testing to be carried out where practicable on existing-installations ......... ( protective-conductor(s)
Earth fault loop impedance , At the following positions :
- origin of the installation .
- distribution boards .
- accessible socket-outlets .
- extremity of radial circuits . ( contd )

R/P 27 . Electrical-installation ( abbr : Installation ) An assembly of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes .

 

[Richard Burns]

For Amberleaf
Diagrams


General


1) Introduction
2) Identification of site services
3) Requirements of BS-7671
3.1 ) Simple installations
3.2 ) Large complex installations


Introduction
Every electrical installation should be provided with appropriate documentation for operational, maintenance, fault finding, inspection, testing and safety reasons. Such documentation, for example, might include:


- single line (or schematic) diagrams
- circuit charts or circuit schedules
- certification and reports
- information for satisfying the relevant parts of the Electricity at Work Regulations 1989 (EWR), such as risk assessments, method statements and isolation procedures, as appropriate


This topic addresses the requirements of BS-7671 for providing diagrams for identification of circuits and equipment in electrical installations.


Identification of site services
For most industrial and commercial installations it is important to be able to identify exactly where hidden services, such as supply cable routes, water services and gas services are located. Without such identification, any site excavation work could cause damage to those services and, more importantly, cause injury or death to persons carrying out such works. Accurate records, including drawings, should preferably be made at the time services are being installed before trenches are backfilled and hidden from view. However, such records are not generally required for the purpose of identifying services in installations in domestic premises.
Where required, cable routes should be identified on drawings to accurately record their position. This may be achieved, for example, by recording the distance from some fixed object that is not expected to change for the foreseeable future, such as a building. A typical drawing showing the position of cable routes and other services is shown in Fig 1.


Example of site layout diagram identifying routes and positions of cables and other services

Requirements of BS-7671


A legible diagram, chart or table or equivalent form of information is required by Regulation 514.9.1 to indicate:


i) the type and composition of each circuit (points of utilisation served, number and size of conductors, type of wiring)
ii) method used for protection against electric shock for compliance with Regulation 410.3.2
iii) the information necessary for the identification of each device for performing the functions of protection, isolation and switching, and its location
iv) any circuit or equipment vulnerable to a particular test, such as computer and communications equipment


for simple installations the foregoing information may be given in a Schedule , A durable copy of the schedule relating to a distribution board shall be provided within or adjacent to each distribution board .


There are several ways of providing the aforementioned information depending on whether the installation is simple or a more complex one. Examples of how to provide the information required by Regulation 514.9.1 for a simple installation and a complex installation are given in items 3.1 and 3.2, respectively.


3.1. Simple installations
For smaller installations, such as in a domestic premises, the information required by Regulation 514.9 (see item 3) may be provided in a circuit schedule. In such cases, the schedule should be legible and be adequately protected from damage or deterioration, for example, by enclosure in a clear plastic folder. Nevertheless, the completed schedule should be fixed within or adjacent to the distribution board or consumer unit. A typical example of a schedule, using a copy of the Schedule of Test Results, based on the model form given in Appendix 6 of BS-7671 is shown in Fig 2 .
Example of completed Schedule of Test Results based on model form in Appendix 6 of BS-7671



3.2. Large complex installations
Providing a completed copy of one or more circuit schedules is unlikely alone to be sufficient for large complex installations, such as an installation in industrial or commercial premises. For those installations, comprehensive information, including site layout diagrams, schematic diagrams, circuit diagrams, cable route plans, as-fitted diagrams are generally required to accompany a series of circuit schedules (refer item 3.1). An example of a typical single-line diagram showing such additional information is shown in Fig 3.
Example of single-line diagram showing installation layout

Diagrams .. 514.9

 

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What's in a Question . ??

Domestic accommodation - general .. Change of occupancy / 10 years .
Domestic accommodation - rented house and flats .. Change of occupancy / 5 years .

GN-3 3.5. Routine checks
Electrical installations should not be left without any attention for the periods of years that are normally allowed between formal inspections . In domestic premises .. refer

Q) An domestic installation has been in use for 10 years . Which test procedure is most appropriate
i) minor works
ii) initial verification

Recommended initial frequencies of inspection of electrical installation(s) .. Note 8 .

A) iii) periodic inspection & test ..
GN-3 table 3.2. Maximum period between inspections & testing .

8 , The person carrying out subsequent inspections may recommend that the interval between future inspections be increased or decreased as a result of the findings of their inspection .

10 , The Landlord & Tenant Act 1985 requires that properties under the Act have their services maintained . Periodic inspection & testing is the IET recognised method of demonstrating this .

iv) portable appliance testing

3.7. Frequency of periodic inspections
Extracts :

In short the inspector being a competent person should apply engineering judgement when deciding upon intervals between inspection and testing an installation and may use the recommendations of table 3.2.

in the case of domestic & commercial premises , a change in occupancy of the premises may necessitate additional inspection and testing .

The formal inspections should be carried out in accordance with Chapter 62 of BS-7671:
621.2. This requires an inspection comprising a detailed examination of the installation , carried out without dismantling or with partial dismantling as required , together with the appropriate tests of Chapter 61 .

 

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Q) your on your own . C&Gs .. During an inspection and test a dangerous condition is noticed , What is the correct procedure . ??

Q) What does not form part of ( test documentation )

Your Q , This Safety certificate has been issued to confirm .. etc
R/P 392 . (2) This Certificate is only valid if accompanied by the Schedule of Inspections & the Schedule(s) of test Results

re-cap ; ( Generic ) Schedule of test Results

i) Electrical installation certificate .. ( EIC )
ii) Test result schedule
iii) Inspection schedule
iv) designer's specifications ..

 

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Q) What is not acceptable for an Earth-electrode . A) you're call !!

i) Rods and tape
ii) Earth plates
iii) Lead sheath of supplier's cable .
iv) Underground water pipes .

542.2. Earth electrode(s)
542.2.3. Suitable earth electrodes shall be used . The following types of earth electrode are recognized for the purpose of the Regulations :
i) Earth rods or pipes .
ii) Earth tapes or wires .
iii) Earth plates .
iv) Underground structural metalwork embedded in foundations .
vi) Lead sheaths and other metal covering of cables , where not precluded by Regulation 542.2.5.

542.2.5.
The use , as an earth electrode . of the lead sheath or other metal covering of a cable shall be subject to all of the following conditions :
i) Adequate precautions to prevent excessive deterioration by corrosion .
ii) The sheath or covering shall be in effective contact with Earth .
iii) The consent of the owner of the cable shall be obtained .
iv) Arrangements shall exit for the owner of the electrical installation to be warned of any proposed change to the cable which might affect its suitability as an earth electrode .

542.2.6.
A metallic pipe for gases or flammable liquids shall not be used as an earth-electrode . The metallic pipe of a water utility supply shall not be used as an earth-electrode . refer

 

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Manufactures' instructions ( LD3 )
Optical
Ionisation
Heat

Interconnecting Alarms
in the UK it is recommended that the following coloured cores are used .. for example with triple flat 6243Y cable

230V supply .. Brown
Neutral .. Gray / sleeved blue at terminations . ◄
Interconnect .. Black .

 

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528 Proximity of Wiring Systems to Other Services
528.1. proximity to electrical services

Voltage Bands . P/36
Defined in Part 2 BS-7671:

Band I ( ELV ) extra low voltage .
Not exceeding 50V a.c. or 120V ripple-free d.c. whether between conductors or to Earth .

whereas power wiring operating at 230V/400V is classified as Band II .
Low . Exceeding extra-low voltage but not exceeding 1000V a.c. refer .

Section 528 sets out the requirements where cables of different voltage bands are to be run in close proximity , requiring either all associated cables to be rated to the highest voltage present ;

Regulation 528.1 (i) or segregation provided between cables of different bands . (iii) , (iv) , (v) or (vi)

528.1. proximity to electrical services
(i) Every cable or conductor is insulated for the highest voltage present .
(iii) The cables are insulated for their system voltage and installed in a separated compartment of a cable ducting or cable trunking system .
(iv) The cables are installed on a cable tray system where physical separation is provided by a partition .
(v) A separate conduit , trunking or ducting system is employed .

(vi) For a multicore cable , the cores of the Band I circuit are separated from the cores of the Band II circuit by an earthed metal screen of equivalent current-carrying-capacity to that of the largest core of a Band II circuit .

 

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Band II P/36

Band II contains the voltages for supplies to household and most commercial and industrial installations .
Low voltage ( LV ) will normally fall within voltage Band II .

Note : Band II voltages do not exceed 1000V a.c. rms or 1500V d.c.

 

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Further detectors might be necessary if a risk assessment justifies their provision .

Scope
This part of BS-5839 gives recommendations
The recommendations apply to both new & existing domestic premises.

Fire detection and fire alarm systems for buildings

BS-5839-6 : Fire detection and fire alarm systems for buildings , Part - 6 Code of practice for design , installation . commissioning and maintenance of fire detection and fire alarms systems in domestic premises .

Normative References
The following references have been amended;

BS 5839-1:2013, Fire detection and fire alarm systems for building(s) Part - 1: Code of practice design, installation, commissioning and maintenance of systems in non-domestic premises