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New or rewired domestic and similar installations

Q1.1

Does the 17th Edition require all 13 A socket-outlets in domestic premises to be RCD-protected?
For new installations and rewires in domestic premises, all socket-outlets need to have additional protection by RCD, except perhaps for those intended to supply particular items of equipment such as freezers. Any socket-outlet not having RCD protection needs to be specifically labelled or otherwise suitably identified to indicate its intended use, such as ‘freezer only’. However, if the wiring to a dedicated socket-outlet is concealed in a wall or partition at a depth of less than 50 mm, or if the internal construction of the wall or partition includes metallic parts other than metallic fixings, the circuit will still need to be suitably protected (by RCD or other means).
Regulation number(s)
- 411.3.3
- 522.6.101
- 522.6.102
- 522.6.103
Q1.2

The 17th Edition requires most if not all circuits in domestic premises to be RCD-protected. There have been a number of suggestions as to how the consumer unit may best be configured to comply with the Regulations, the most common being a main switch with RCBOs protecting each individual circuit. However, another suggestion favours a main switch with two RCDs protecting separate DIN rails. If careful consideration is given as to what each bar will control in the way of upstairs and downstairs lighting and power circuits, will this configuration comply?
Yes, as long as the division of final circuits between the RCDs is carefully considered so as to minimize the consequences of unwanted tripping. Separate RCD protection is not necessarily required for each circuit of an installation but, in order to minimize the likelihood and consequences of tripping, a single (‘front end’) RCD should not be used to protect all the circuits.
Regulation number(s)
- 314.1
Q1.3

The 17th Edition does not now define a zone 3 in a bathroom or shower room. What electrical equipment and accessories can be installed in the area between 0.6 m and 3.0 m from the edge of the bath or shower basin? Moreover, what minimum degree of IP protection are manufacturers likely to recommend?
There is no change from the 16th Edition requirements – that is, the general rules apply. The manufacturer’s installation instructions must always be followed.
Regulation number(s)
- 512.2
- 134.1.1
Q1.4

Do ‘meter tails’ concealed in walls or partitions need to be protected in accordance with Regulations 522.6.101 and/or 522.6.103?
Yes. Meter tails concealed in a wall or partition at a depth of less than 50 mm from a surface must be protected in accordance with Regulation 522.6.101 Also, irrespective of the depth from a surface, meter tails concealed in a wall or partition having internal metallic parts (except nails and screws, etc) are subject to the requirements of Regulation 522.6.103

However, additional protection for meter tails by means of an RCD is not an acceptable option in respect of Regulation 522.6.102 (which in consequence rules out reliance on 522.6.101(v), routing in the ‘safe zones’ alone), or in respect of Regulation 522.6.103(v). Also, for TT systems, the only option remaining is to provide suitable mechanical protection (that is, to comply with Regulations 522.6.103(iv) and/or 522.6.101(iv) as appropriate).
Regulation number(s)
- 522.6.101
- 522.6.103
- 314.1
- 314.2
Q1.5

Where the Regulations specify additional protection by RCD, does this include RCBOs?
Yes. Where the generic term ‘RCD’ is used, it refers to most types of residual current device including RCBOs (Residual current-operated circuit-breakers with integral overcurrent protection), RCCBs (Residual current-operated circuit-breakers without integral overcurrent protection) and SRCDs (Socket-outlets incorporating a residual current device). For the purposes of the Regulations, it does not include PRCDs (Portable residual current devices).
Regulation number(s)
- 411.3.3
Q1.6

Does boiler pipework need to have additional equipotential bonding for electrical safety reasons?
There is no specific requirement in the Regulations for boiler pipework to be supplementary bonded. However, such bonding may be called for in the boiler manufacturer’s instructions, in which case BS 7671 requires those instructions to be followed (Regulation 510.2 refers). Any stated requirement for additional bonding that is considered to be unnecessary should be queried with the manufacturer concerned, and amended installation instructions requested.
Regulation number(s)
- 411.3.3
Q1.7

Does the dispensation in Regulation 701.415.2 to omit supplementary bonding in a location containing a bath or shower apply to TT systems?
Yes
Regulation number(s)
- 701.415.2
Q1.8

If the mains supply cable to a fixed appliance such as a flat screen TV is concealed in a wall or partition at a depth of less than 50 mm, does the 17th Edition require the lead to be RCD-protected in accordance with Regulation 522.6.102 even though it’s connected by means of a plug and socket?
Yes. The risk of penetration by a nail or screw is the same as for other concealed cable. Also, if the wall or partition has internal metallic parts (except nails and screws, etc), RCD protection in accordance with Regulation 522.6.103 is required irrespective of the depth of the cable from the surfaces.
Regulation number(s)
- 522.6.102
- 522.6.103
Q1.9

To overcome thermal insulation issues, is it permissible to design a ring final circuit using 2.5 mm² cable protected by a 20 A protective device?
Yes, if the effective current carrying capacity of the cable is at least 12.5 A (20 A × 20/32), so as to effectively have the same ‘deemed to comply status’ as Regulation 433.1.103 gives to 30 A and 32 A ring final circuits.
Regulation number(s)
- 433.1.103
Q1.10

Should signal amplifiers mounted at high level on television aerials where they might be struck by lightning be main bonded?

There is no specific requirement in BS 7671 but, if there is considered to be a significant risk of a lightning strike, the advice of a lightning protection specialist should be sought.
Q1.11

I am still working on an electrical installation that was designed before Amendment 1 to BS 7671: 2008 came into full effect on 31 December 2011. To which requirements should the installation be inspected, tested, verified and certificated?

An installation designed before 31 December 2011 should be inspected, tested, verified and certificated to BS 7671: 2008, that is to the original version prior to the amendment.
Q1.12

What types of mechanical protection provide sufficient protection against penetration by nails, screws and the like?
As an example, steel of 3 mm minimum thickness is generally considered to provide sufficient mechanical protection, except where shot-fired nails are likely to be used.
Regulation number(s)
- 522.6.101
- 522.6.103
Q1.13

Five flats are fed individually from five ‘sub-mains’ originating at the main intake position. The five gas and water meters are main bonded at the main intake position. Do we still need to provide main bonding in each of the flats?
Whilst main protective bonding is required at the main intake position, it is good practice also to provide main protective bonding in each flat even though, in this case, the origin of each installation could be considered to be at the main intake position.
Regulation number(s)
- 411.3.1.2
Q1.14

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

For a domestic installation complying with the 17th Edition where all the final circuits are RCD-protected, an RCD main switch is no longer required, provided that the consumer unit is of all insulated construction.
Q1.15.

Does the device that has to be provided for switching off a bathroom extract fan for mechanical maintenance need to be located adjacent to the fan?
No, but the device does need to be so placed and marked as to be readily identifiable and convenient for the intended use
Regulation number(s)
- 537.3.2.4
Q1.16.

Can accessories and electrical equipment such as socket-outlets and under-cupboard lighting be fixed to fitted kitchen units?
Yes, provided that they are securely fixed to rigid parts of the units that are not demountable or otherwise liable to be disturbed in normal service. However, care must be taken to comply with all the relevant requirements of BS 7671, including accessibility for inspection, testing and maintenance, and provision of adequate protection against damage (by impact or water for example) for the accessories, equipment and associated wiring.
Regulation number(s)
- 530.4.2
Q1.17

When a Grade D fire detection and alarm system to BS 5839-6: 2004 is protected by an RCD, should the RCD operate independently of any circuits supplying socket-outlets or portable equipment?

There are no particular requirements or limitations in BS 5839-6 concerning the use of RCDs with Grade D fire detection and alarm systems.

For Grade D systems, which comprise one or more mains-powered smoke alarms each with an integral standby power (such as typical domestic smoke alarm with battery), BS 5839-6 simply recommends that the mains supply to the smoke and/or heat alarms should take the form of either:

i) an independent circuit at the dwelling’s main distribution board, in which case no other electrical equipment should be connected to the circuit (other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke and/or heat alarms), or

ii) a separately electrically protected, regularly used local lighting circuit.

We recommend option ii) on the grounds that disconnection of the supply to the fire detection and alarm system will be more readily noticed. In our opinion ‘separately electrically protected’ does not preclude sharing an RCD with several other circuits where this is permitted by BS 7671.
Q1.18

Does the 17th Edition permit connection of smoke alarms to an adjacent lighting circuit taking into account Regulation 560.7.1, which states that circuits of safety services shall be independent of other circuits?
Yes. The particular requirements of BS 5839-6 take precedence over the general requirements of BS 7671.
Regulation number(s)
- 110.1
Q1.19

Does the R1 + R2 test confirm the correct polarity of a radial circuit?
No, not on its own. Whilst the test can provide an indication of polarity, it needs to be combined with inspection and further testing as required by Part 6 of BS 7671: 2008
Regulation number(s)
- 611.3
- 612.6
Q1.20

Appendix 15 of BS 7671: 2008 gives advice on ring final circuits and sharing/spreading the load around the circuit. Item (iii) suggests that cookers, ovens and hobs over 2 kW should be on their own dedicated circuit. Why can’t ovens of less than 3 kW be connected to a ring final circuit via a suitable connection point such as a socket-outlet or fused connection unit?
Appendix 15 is intended to give guidance only. Such connection is not prohibited, provided that no part of the ring final circuit will be overloaded as a result.
Regulation number(s)
- 433.1.5
Q1.21

Does Regulation 522.6.102 require additional protection by RCD for cables of SELV and PELV circuits concealed in walls and partitions at a depth of less than 50 mm?

No. Due to an oversight, an agreed clarification was omitted from the published version of Amendment 1 to BS 7671: 2008. Regulation 522.6.102 should have read:
‘Where Regulation 522.6.101 applies and the installation is not intended to be under the supervision of a skilled or instructed person, a cable installed in accordance with Regulation 522.6.101(v), and not also complying with Regulation 522.6.101 (i), (ii), (iii), (iv) or (vi), shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.’
Q1.22

In locations containing a bath or shower, is Regulation 701.411.3.3, which requires additional protection by RCD, intended to apply to circuits of SELV, PELV and/or FELV (other than to the cables supplying the sources at Low Voltage if installed within the location)?
No. The requirement for additional protection applies only to Low Voltage circuits
Regulation number(s)
- 701.411.3.3
Q1.23

In ‘smith construction’ or ‘truss’ dwellings, metal frame parts in the loft area are likely to be bolted to structural metalwork embedded in the ground and hence are likely to be extraneous-conductive-parts. Do they require main protective bonding?
If the metallic structure falls within the definition of an extraneous-conductive-part given in Part 2 of BS 7671, it is required to be main bonded.
Regulation number(s)
- 411.3.1.2
Q1.24

Is it necessary to verify voltage drop during initial verification?
Verification of voltage drop is not normally required unless there is considered to be a voltage drop problem.
Regulation number(s)
- 612.14
Q1.25

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

Yes. It is necessary to check that all connections are tight, and any specific installation instructions must also be followed.
Q1.26

In a location containing a shower, what is the horizontal limit of zone 1 for showers without a basin?
The limit of zone 1 horizontally is 1.2 m from the centre point of the fixed water outlet (the end of the rigid pipe of the fixed water installation) on the wall or ceiling, irrespective of whether the shower head is fixed or on the end of a flexible hose. Beyond zone 1, the general rules of BS 7671 apply, including Regulation 512.2 concerning external influences. In particular, the IP rating of any electrical equipment must be adequate.
Regulation number(s)
- 701.32.3
- 512.2
Q1.27

Regulation 560.7.7 requires cables for safety circuits, other than metallic screened fire-resistant cables, to be adequately and reliably separated from other circuit cables. In addition to mineral insulated cables, what cables would be exempted from this separation requirement?
Soft-skinned cables to BS 7629-1: 2008 would be exempted from the separation requirements as they have a metallic screen and their survival in a fire has been tested in accordance with BS EN 50200. However, cables to BS 8436: 2004 would not be exempted as the product standard does not require their fire resistance to be tested. Irrespective of the above, BS 5839-1 recommends that, for a fire detection and alarm system complying with that standard, the circuits of fire alarm systems should be segregated from the cables of other circuits to minimize the potential for those other circuits to cause malfunction of the fire alarm system.
Regulation number(s)
- 560.7.7
Q1.28

Is it acceptable to use an unfixed connector block to join the line or neutral conductors at a light switch?

Yes
Q1.29

As the designer of an installation, am I allowed to rely on the RCD element of an RCBO to provide for fault protection in order to allow for loop impedance values greater than given in Table 41.3?
Yes, so long as all the other applicable requirements of the 17th Edition (as amended) are met, including those for protection against overload and short circuit.
Regulation number(s)
- 411.4.4
- 411.4.5
- 411.4.9
Q1.30

Are there any particular requirements relating to the mounting height or location of consumer units for electrical installations in new dwellings?
The provision of access to consumer units is not specifically covered by Building Regulations or BS 7671. However, consumer units need to be so located as to enable reasonable access by the users, including for the purpose of testing the RCDs at regular intervals, and in case of emergency.

BSI Draft for development DD 266: 2007 – Design of accessible housing: Lifetime homes – Code of practice, explains how, by following the principles of inclusive design, general needs housing can be made sufficiently flexible and convenient to meet the existing and changing needs of most households, and so give disabled and older people more choice over where they live.

Amongst other things, the code of practice recommends that meters and consumer units should be mounted 1200 mm to 1400 mm from the floor so that the readings and switches can be viewed by a person standing or sitting, and should be positioned to be accessible.
Regulation number(s)
- 132.12
- 341.1
- 513.1
Q1.31

Is the space within an airing cupboard in a bathroom or shower room that would otherwise be in a particular zone were it not for the cupboard door, considered to be within that zone?
No, unless the cupboard door does not effectively limit the extent of the location. However, where an airing cupboard opens into zone 1 or zone 2, we recommend that circuits supplying equipment in the airing cupboard are be provided with additional protection in accordance with Regulation 415.1.1.
Regulation number(s)
- 701.32.1
- 701.411.3.3
Q1.32

What is the correct sequence for testing RCDs?

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

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

In any case, the test button should be operated last in the sequence.
Q1.33

Is it acceptable to mount a cooker switch in a kitchen cupboard that is adjacent to the cooking appliance?

Yes, provided the switch is located so as to be readily accessible.
Q1.34

Is a cooker switch or cooker control unit required to be provided as means of emergency switching for an electric cooker?

Generally, cooker switches and cooker control units are provided as a local means of isolation and switching off for mechanical maintenance.

In most cases, the controls incorporated in a cooker can be used to remove the source of heat if danger arises.

However, a cooker switch or cooker control unit may also be provided as a means of emergency switching if the designer of the electrical installation decides that it is necessary, in which case it must be located so as to be readily accessible.
Q1.35

Where the earth fault loop impedance for a circuit exceeds the maximum Zs for the overcurrent device, is it permissible to use an RCD?
Yes.
Regulation number(s)
- 411.4.4
- 411.5.2
Q1.36

In the model Schedule of Inspections in BS 7671, ‘Presence of supplementary bonding conductors’ is included under both ‘Automatic disconnection of supply’ and ‘Additional protection’. Why are there two boxes with the same meaning and where should one be ticked rather than the other?
Supplementary bonding may be provided for either reason. The appropriate box(es) should be completed.
Regulation number(s)
- 411.3.2.6
- 415.2
Q1.37

In the model Schedule of Inspections in BS 7671, what needs to verified in order to confirm the ‘Presence of earthing arrangements for combined protective and functional purposes’?
To verify that the requirements of Regulation 543.5.1 relating to combined protective and functional earthing, and Regulation 543.7 relating to high protective conductor currents, have been met as appropriate.
Regulation number(s)
- 543.5.1
- 543.7
Q1.38

In the model Schedule of Inspections in BS 7671, what has 'Presence of adequate arrangements for alternative sources' to do with automatic disconnection of supply?
To confirm that the fault protection arrangements for alternative sources of supply have been met.
Regulation number(s)
- 551.4
Q1.39

In the model Schedule of Inspections in BS 7671, under ‘Automatic disconnection of supply’, where applicable, what needs to be verified to confirm the requirements for FELV have been met?
It needs to be verified that the supplementary provisions described in Regulations 411.7.2 and 411.7.3 have been applied to ensure basic protection and fault protection.
Regulation number(s)
- 411.7
Q1.40

The model Schedule of Inspections in BS 7671 would be used as part of an Electrical installation certificate where a consumer unit was installed, but no circuit cables were replaced. All boxes have to be a tick or n/a. What then do you need to do with the boxes to do with cable routes in prescribed zones?

As the installer of the consumer unit has insufficient knowledge of the cable routes, the box ‘Routing of cables in prescribed zones’ should be marked ‘n/a’.
Q1.41

Does the requirement for a warning notice in accordance with Regulation 537.2.1.3 apply to a two-gang light switch fed by two separate circuits in a domestic situation?

Yes, although it is recognised that the requirement may be difficult to comply with in some situations. The Forum intends to raise this issue with the BS 7671 Committee.
Q1.42

Can I use an electrical connector having ‘push fit’ connections that the manufacturer claims are maintenance free in an area that will be inaccessible when the installation is complete?

Not necessarily. Not all types or designs of push fit (screwless-type) clamping units comply with the requirements of Regulation 526.3 (vi).

If the connector will be inaccessible when the installation is complete, it must comply with BS 5733 for a maintenance-free accessory, be marked with the ‘MF’ symbol indicated in Regulation 526.3 (vi), and be installed in accordance with the manufacturer's instructions.

BS 5733 requires, for example, tests for resistance to ageing, cyclic loading, overload, fault current and vibration.
Q1.43

Is a socket-outlet allowed under a bath behind screwed panels?
No. Socket-outlets in a bathroom (other than SELV socket-outlets and shaver supply units) are not permitted within 3 m of zone 1
Regulation number(s)
- 701.512.3
Q1.44

After replacing a consumer unit, it is found that there is a shared neutral between the upstairs and downstairs lighting circuits. Would it comply with BS 7671 if I put the lighting onto one circuit to avoid the RCD tripping?
The Electrical Safety Council’s Best Practice Guide No 6 (Consumer unit replacement in domestic premises) sets out a procedure to help avoid such foreseeable circumstances.

In any event, the shared neutral situation must be corrected to remove the electric shock hazard.

Preferably each circuit should be provided with its own neutral to satisfy Section 314.

However, where this is not practicable, the two lighting circuits sharing the neutral may be connected to a single protective device (creating a single circuit), provided that the circuit is suitable for the connected load.
Regulation number(s)
- 314
Q1.45

Are the relevant tests of Regulations 612.2 to 612.13, for example continuity of protective conductors and earth fault loop impedance, applicable to parts of systems such as room and cylinder thermostats, motorized valves and programmers?
Yes. Automatic Disconnection of Supply (ADS) is a commonly-used protective measure against electric shock in such systems. The continuity of protective conductors to each point should be confirmed. The value of R₂ or (R₁ + R₂) may be used to estimate the maximum earth fault loop impedance of each control circuit for verification purposes.

Insulation resistance tests should also be carried out, precautions having been taken to avoid damage to any electronic components, and remembering that it is essential that the protective conductors are connected to the general mass of the Earth during line/Earth insulation resistance testing.

The results should be recorded on a schedule of test results.
Regulation number(s)
- 411.3.1.1
- 411.3.2
- 612.3
- 612.9
Q1.46

Is it appropriate to use a multimeter or a multifunction test instrument to prove equipment dead?

The procedure for proving dead should be by use of a proprietary test lamp or two-pole voltage detector as recommended in HSE Guidance Note GS38, Electrical test equipment for use by electricians. The use of multimeters, makeshift devices and noncontact voltage indicators (voltage sticks) is not advised for voltage detection as such use has caused accidents. (See also ESC Best Practice Guide No 2)
Q1.47

Would three layers of standard metal capping be regarded as sufficient mechanical protection (as required by 522.6.101 indent (iv)) for a cable concealed in a wall or partition?

No. Such use of capping would be outside its intended application.
Q1.48

With consumer units getting larger, there may not always be sufficient space to mount them horizontally. Is it permissible to mount them vertically, provided the manufacturer is in agreement?
Yes, where documentation is obtained from the consumer unit manufacturer confirming that the specific mounting orientation is suitable and complies with BS EN 60439-3. Where catalogue products cannot fulfil the installation requirements, manufacturers can be contacted to discuss tailored solutions.

It is essential that any label, RCD test instructions etc remain legible.
Regulation number(s)
- 510.3
- 511.1
Q1.49

Does the main switch in a consumer unit have to be such that ON is up and OFF is down, or may the OFF position be up, or horizontally left or right?
The switch requires clear labelling or indication for the ON and OFF positions, regardless of orientation.
Regulation number(s)
- 537.2.2.2
Q1.50

Is it permissible to install a consumer unit more than 3 m from the distributor’s service head?

Yes, in certain circumstances. Distributors generally accept a maximum of 3 m from the service head. Where the tails need to be longer, the distributor may require a means of isolation to be provided within 3 m of the service head. Any particular requirements should be ascertained in advance from the distributor.
Q1.51

For an electric shower, can the copper cold water supply pipe be contained in the same trunking as the insulated and sheathed BS 6004 supply cable?
Yes. The close proximity of the cold water pipe to the wiring system is unlikely to be detrimental to the cable, for example due to heat or condensation.
Regulation number(s)
- 528.3
Q1.52

Is it permissible to use equipment (such as circuit-breakers, RCDs, main switches etc) made by one manufacturer in a consumer unit or distribution board made by another manufacturer?
Usually not. Manufacturers’ instructions for consumer units and distribution boards generally advise against this for technical reasons (such as potential overheating). Equipment from different manufacturers should not be mixed unless documentation is obtained from the consumer unit or distribution board manufacturer which confirms that the specific mixed arrangement is suitable for use in an assembly conforming to BS EN 60439-3. Further guidance can be found at www.beama.org.uk
Regulation number(s)
- 510.3
- 511.1
- 512.1.5
Q1.53

Regulation 415.2.1 of BS 7671 makes reference to supplementary protective bonding conductors between simultaneously accessible exposed-conductive-parts and extraneous-conductive-parts. What dimension limits simultaneously accessible?
BS 7671 does not define a dimension to qualify “simultaneously accessible” with respect to supplementary bonding.

However, with respect to prevention of unintentional contact with live parts, the note to 417.3.1 states that two parts are deemed to be simultaneously accessible if they are not more than 2.50 m apart.

Therefore, it is reasonable that with respect to supplementary bonding, parts greater than 2.50 m apart may be considered not to be simultaneously accessible.
Regulation number(s)
- 417.3.1
Q1.54

What should be inserted in the column ‘Maximum disconnection times permitted by BS 7671’ where an RCD or RCBO is connected to a circuit?
The ‘Maximum disconnection time permitted by BS 7671’ column is associated with fault protection and the disconnection time to be inserted in that column should be determined in accordance with Regulation 411.3.2.2 (Table 41.1), 411.3.2.3 or 411.3.2.4, as applicable. www.beama.org.uk
Regulation number(s)
- 411.3.2.2
- 411.3.2.3
- 411.3.2.4
Q1.55

The wiring diagram forming part of the installation instructions for a bathroom fan shows a fuse for overload protection of the fan. How should I comply with the fusing requirement?
If the fusing requirement is not complied with and, for example, the fan stalls, there may be a risk of fire. Install a fused connection unit in the supply to the fan.

Regulation numbers: 134.1.1, 510.3
Regulation number(s)
- 134.1.1
- 510.3
Q1.56

What inspection, testing and certification should a contractor undertake when carrying out a like-for-like replacement of an accessory or an item of current-using equipment?

An inspection should be carried out to ascertain that the existing cable supplying the item is adequate. Tests of polarity, Zs and, where appropriate, correct RCD operation should, as a minimum, also be carried out.

It is recommended that the results are recorded for the benefit of both the customer and the contractor. A suitable minor works form or works order may be used to record the details of the inspection and testing.
Q1.57

What should I do if the manufacturer’s installation instructions for a product conflict with the requirements of BS 7671, or include inappropriate or unnecessary technical requirements?

Any installation instructions considered to be technically unsound should be queried with the manufacturer and/or referred to the electrical contractor’s registration body for information.
Q1.58

A water utility service enters an apartment block in plastic and then metal branches feed individual apartments. To which location(s) should main protective bonding be provided?
Main protective bonding is required between each metallic branch as it enters an apartment and the Main Earthing Terminal in that apartment, unless it has been proven that the metallic pipework is not an extraneous-conductive-part.
Regulation number(s)
- 544.1.2
Q1.59

Do blanks fitted in a distribution board or consumer unit that can be removed without the use of a tool or key comply with the requirements of BS 7671 with regard to access to live parts?
If the distribution board or consumer unit is fitted with blanks that can be removed without the use of a tool or key resulting in live parts being made accessible to touch, at least one of the following requirements must be complied with (in addition to the manufacturer’s instructions):
- The lid over the blanks can be secured and opened only by use of a tool or key
- The distribution board or consumer unit is in a locked location accessible only by key held by a responsible person
- The distribution board or consumer unit is located in a generally inaccessible area (in which case compliance with other relevant requirements (such as accessibility for operation, maintenance and repair) needs to be confirmed)
If the distribution board or consumer unit is located in a generally accessible area and has a flap-type lid with no securing device, the blanks fitted must be of a type that can be removed only by opening the front cover, using a tool or key.
Regulation number(s)
- 134.1.1
- 416.2.3
- 416.2.4
Q1.60

In a building where semi-rigid gas pipe is installed, where is the appropriate position to connect the main protective bond if the gas meter is:

(a) internal to the building

(b) external to the building
No attempt should be made to make a bonding connection directly to semi-rigid pipework.

(a) Where the gas meter is installed inside the premises, the semi-rigid pipework will normally end at the meter and so the bonding connection should be made as normal to the consumer’s hard metal pipework within 600 mm of the meter outlet union and before any branch pipework.

(b) Where the meter is external to the premises in a wall-mounted or semi-concealed meter box, the bonding connection should be made, where practicable, within 600 mm downstream of the point at which the semi-rigid pipework changes to hard metal pipework and before any branch pipework.
Regulation number(s)
- 411.3.1.2(i)
- 544.1.2
Q1.61

Where an RCD is installed to provide additional protection for a circuit, what is the maximum value of Zs permitted by BS 7671 for the circuit?
If, by design, fault protection is provided by a fuse, circuit-breaker or the overcurrent characteristic of an RCBO, the maximum Z_s permitted by BS 7671 for U₀ of 230 V can be taken from Table 41.2, 41.3 or 41.4, as applicable.

Where, by design, fault protection is provided by an RCD or the RCD element of an RCBO, the maximum Z_s permitted by BS 7671 for U₀ of 230 V can be taken from Table 41.5.
Regulation number(s)
- 411.4.4
- 411.4.5
- 411.4.9
Q1.62

Is it permissible to route cables through a room containing a bath or shower if they are not associated with that location?

Yes.
Q1.63

Is it necessary to install surge protective devices (SPDs) in domestic and similar premises?
Generally, no.

However, where a risk assessment is carried out and this indicates that unacceptable consequences exist, such as to human life (as a result of damage to essential medical equipment, for example), SPDs must be installed. In addition, where the consequences of equipment failure due to an overvoltage are deemed to be unacceptable after discussion with the customer, SPD protection should be provided.
Regulation number(s)
- 443.2
Q1.64

In a multicore flexible cable that includes a protective conductor coloured green-and-yellow (having the same csa as the other conductors), can the protective conductor be used as a live conductor if it is suitably overmarked at each end of the cable?
Yes. In a multicore cable, a core having green-and-yellow insulation may be overmarked or otherwise identified for use as a live conductor.
Regulation number(s)
- 514.4.2
Q1.65

Can a single-core cable having green-and-yellow insulation be used for any purpose other than a protective conductor?
No (with one specific exception). Single-core cables having green-and-yellow insulation must not be overmarked or otherwise identified, and must not be used for any purpose other than a protective conductor. The only exception is where such a cable is used as a PEN (combined protective and neutral) conductor, when blue markings must be provided at the terminations.
Regulation number(s)
- 514.4.2
- 514.4.3
Q1.66

The external earth fault loop impedance at an installation is so high that it seems likely that there is a fault on the distribution system. Is it sufficient to install RCDs in the installation to enable the required disconnection times to be achieved?

No. An excessively high external earth loop impedance value would need to be brought to the attention of the Distribution Network Operator (DNO).