New, rewired and similar installations

This section incorporates questions relating to:

• New or rewired domestic and similar installations
• Alterations and additions in domestic and similar premises

You may notice that some numbers are missing from the Q&A. This is deliberate. The regulations are constantly updated and as questions become out of date, we remove them but do not renumber, as we are aware that visitors to the site will note specific numbers for future reference.

If you have any queries, please contact enquiries@electricalsafetyfirst.org.uk with "Wiring Regulations" as the subject line of your message.

Q1.1. Do the Wiring Regulations require all 13 A socket-outlets in a dwelling to be RCD protected?

Yes.

Regulation number(s):

411.3.3

Q1.2. BS 7671 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. What electrical equipment and accessories can be installed in the area beyond zone 2 of a location containing a bath or shower basin?

Socket-outlets other than a SELV socket-outlet or a shaver supply unit are not permitted within 2.5 m horizontally from the boundary of zone 1.  In all other cases, only the general rules apply, in that equipment shall be of a design appropriate to the situation in which it is to be used or its mode of installation shall take account of the conditions likely to be encountered.

Manufacturer’s installation instructions shall be taken into account when selecting equipment.

Regulation number(s): 

• 134.1.1
• 512.2 
• 701.512.3

Q1.4. Do ‘meter tails’ concealed in walls or partitions need to be protected in accordance with Regulations 522.6.202, 522.6.203 and/or 522.6.204?

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 522.6.202. 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 522.6.203.

Regulation number(s):

• 522.6.202
• 522.6.203
• 522.6.204 

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 taken into account (Regulation 510.3 refers). Any stated instruction for additional bonding that is considered to be unnecessary should be queried with the manufacturer concerned, and amended installation instructions requested.

 

Regulation number(s):

• 510.3

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 50mm, does BS 7671 require the lead to be RCD-protected in accordance with Regulation 522.6.202 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 any other concealed cable. Also, if the wall or partition has internal metallic parts (except nails and screws, etc.), RCD protection in accordance with Regulation 522.6.203 is required irrespective of the depth of the cable from the surfaces.

Regulation number(s):

• 522.6.202
• 522.6.203

Q1.9 To overcome thermal insulation issues, is it permissible to protect a ring final circuit using 2.5 mm² cable using 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 433.1.204 gives to 30 A and 32 A ring final circuits.

Regulation number(s):

• 433.1.204

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

In the absence of a relevant product standard, e.g. British Standard, the designer should obtain suitable evidence from the manufacturer that any product selected for the purpose is suitable to prevent 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 or similar fixing methods are likely to be used.

Regulation number(s):

• 522.6.204(iv)

Q1.12 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

Q1.13 For a domestic installation forming part of a TT system, where all the final circuits are RCD-protected (i.e. by RCBOs), is an RCD main switch (such as a 100 mA time-delayed device) required in the consumer unit?

No.

Q1.14 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

Q1.15 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

Q1.16 When a Grade D fire detection and alarm system to BS 5839-6: 2013 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.

Q1.17 Does BS 7671 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

Q1.18 Appendix 15 of BS 7671 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):

433.1.204

Q1.19 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

 

Q1.21 Where torque settings for connection tightness are specified in manufacturers’ instructions, does this mean installers must confirm these settings during work using a torque driver?

Regulations 134.1.1 and 510.3 state that manufacturers’ instructions are to be taken into account during installation work. It is necessary to check that all connections are tight, and the use of a torque screwdriver is one way of confirming this.

Q1.22 In a location containing a shower with a demountable shower head but no shower basin (e.g. a wet room), what is the horizontal limit of zone 1?

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.

Note: There is no zone 2 for showers without a basin.

Regulation number(s): 

• 701.32.3
• 512.2

Q1.23 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

Q1.24 Is it acceptable to use an unfixed connector block to join the line or neutral conductors at a light switch?

Yes.

Q1.25 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 BS 7671 are met, including those for protection against overload and short circuit.

Regulation number(s): 

• 411.4.4
• 411.4.5
• 411.4.204

Q1.26 Are there any particular requirements relating to the mounting height or location of consumer units for electrical installations in new dwellings?

Yes, the requirements for mounting height are different for each of the devolved governments as follows:

England – Approved Documents P and M call for consumer units to be mounted so that the switches are 1350-1450 mm above finished floor level.

Wales – Approved Documents P and M do not provide specific information on mounting height for consumer units but controls that require close vision are required to be located between 1200-1400 mm above finished floor level.

Scotland – Technical Handbook D10 does not provide specific information on mounting height for consumer units but requires electrical controls (which would include consumer units) to be positioned not more than 1200 mm above floor level, unless the need for a higher location can be demonstrated. Whilst there is no minimum height indicated it would seem sensible to locate consumer units at least 900 mm above floor level (the lower limit for light switches).

Northern Ireland – Technical Booklet R does not provide specific information on mounting height for consumer units but for controls that require close vision are required to be located between 1200-1400 mm above finished floor level.

The British Electrotechnical and Allied Manufacturers’ Association (BEAMA) recommend that for a multi-row consumer unit where compliance with mounting heights of ADM1 above cannot be achieved for all switches thereof, the consumer unit should be mounted such that the bottom row of switches are located between 1350 mm and 1450 mm so that they are out of reach of young children to avoid interference and inappropriate operation.

Q1.27 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 provided with additional protection in accordance with Regulation 415.1.1.

Regulation number(s): 

• 701.32.1
• 701.411.3.3

Q1.28 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 and convenient for use.

Q1.29 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 and convenient for use.

Q1.31 Does the requirement for a warning notice in accordance with Regulation 537.1.2 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. 

Q1.32 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.

Q1.33 Does BS 7671 permit low voltage (230 V) current-using equipment such as a booster pump for a shower to be installed in the space under a bath or shower?

Yes, but certain restrictions apply if the space under the bath or shower is accessible without using a tool because the space is then classed as zone 1.

In zone 1, any low voltage current-using equipment (such as a booster pump for a shower) must be fixed and permanently connected, and the manufacturer’s instructions must confirm that is suitable for installation in that zone.

As with any other item of equipment installed in zone 1, the accessory used to connect it to the supply would need to provide a degree of protection of at least IPX4.

Regulation number(s):

• 701.32.3
• 701.512.2
• 701.55

Q1.34 Where low voltage (230 V) current-using equipment such as a booster pump for a shower is installed in the space under a bath or shower that is accessible only by means of a tool (e.g. bath panel is fixed by screws), is it permitted for the equipment to be connected by means of a plug and socket-outlet installed in that space?

Yes.  As the space under the bath or shower is accessible only by means of a tool, the space is classed as being outside the zones (Regulation 701.32.3 refers).

Consequently, low voltage current-using equipment (such as a shower booster pump) installed in the space need not be permanently connected, and it may therefore be connected by means of a plug and socket-outlet installed in the space.

Regulation number(s):  

• 701.32.3

 

Q1.35 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?

Electrical Safety First's Best Practice Guide No 1 (Replacing a consumer unit in domestic and similar 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

Q1.36 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 61439-3. 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

Q1.37 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.

Q1.38 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 2m or 3m from the service head. Where the tails need to be longer, the distributor may require a means of isolation and/or a protective device to be provided within 2m or 3m of the service head. Any particular requirements should be ascertained in advance from the distributor.

Q1.39 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

Q1.40 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
• 536.4.203

Q1.41 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.

Q1.42 If I replace or install an electric extractor fan connected to a lighting circuit in domestic or similar premises, do I need to provide overcurrent protection specifically for the fan in addition to that provided for the circuit?

Although there is no specific requirement for this in BS7671, account should be taken of the manufacturer's installation instructions, which may or may not require such protection.

Regulation number(s): 

• 134.1.1
• 510.3

Q1.43 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.

Q1.44 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

Q1.45 Do clip-in blanks fitted in a distribution board or consumer unit comply with the requirements of BS 7671 with regard to access to live parts?

Yes, provided that the distribution board or consumer unit conforming to BS EN 60 / 61439-3 is fitted with blanks that are firmly secured in place with sufficient stability and durability to maintain the required degrees of protection and appropriate separation from live parts under normal service conditions. Distribution board or consumer unit manufacturers can supply blanks to meet these requirements.

Note 1: Different manufacturer’s blanks are not automatically interchangeable. Different types of blanks may be specified by the distribution board or consumer unit manufacturer for specific product references, covering old and new ranges. BS 7671 does not deal with requirements for the construction of assemblies of electrical equipment, which are required to comply with appropriate standards. Therefore, the distribution board / consumer unit should conform to the relevant product standard and be installed according to the manufacturer’s instructions; including any clip-in blanks required to complete the enclosure.

Note 2: Metal blanks should be used only where the consumer unit / distribution board manufacturer has confirmed they are suitable for the intended use.

Regulation number(s):

• 113.1
• 134.1.1
• 416.2.3

Q1.46 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 after the meter and before any branch pipework. Where practicable the bonding connection should be within 600 mm of the meter outlet union.

(b)    Where the meter is external to the premises in a wall-mounted or semi-concealed meter box, the bonding connection should be made to the consumer’s hard metal pipework and before any branch pipework. Where practicable this connection should be made at the point of entry to the building.

Regulation number(s):

• 411.3.1.2(i)
• 544.1.2

Q1.47 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?

Where, by design, fault protection is provided by a fuse, circuit-breaker or the overcurrent characteristic of an RCBO, the maximum Zs 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 Zs permitted by BS 7671 for U₀ of 230 V can be taken from Table 41.5.

It should be noted where fault protection is provided by an RCD then an overcurrent protective device shall provide protection against overload and/or short-circuit current. 

Regulation number(s):

411.4.4

411.4.5

411.4.204

Q1.49 Is it permissible to route cables through a room containing a bath or shower if they are not associated with that location?

Yes.

Any low voltage circuits passing through, but not serving, zone 1 or Zone 2 of the location must be provided with additional protection by RCD.

Regulation number(s):

701.411.3.3

Q1.51 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).

Regulation number(s):

N/A

Q1.52 How close can an accessory, such as a light switch or socket-outlet, be installed to a cooker hob?

BS 7671 does not specify a minimum distance between an accessory and a heat source, such as a hob.  However, indent (ii) of Regulation 522.2.1 recognises placing sufficiently far from the source of heat as one method that may be used to protect a wiring system.

When considering what constitutes a suitable distance, it is worth remembering that the sources of heat on a cooker top are usually somewhat inboard from the edge of the appliance.  Another point to remember is that the integral control dials on a cooker are in some cases significantly closer to the source of heat than any accessory affixed to the building fabric, and they do not suffer significant heat damage.

An accessory installed at least 100mm horizontally from the edge of the hob is likely to meet the requirements of BS 7671.  If an accessory is encountered closer to a hob than this during a periodic inspection, engineering judgement will need to be applied to determine whether this is safe. An accessory so located for a considerable time that had not suffered any perceptible heat damage would not warrant a classification code or comment on the Electrical Installation Condition Report.

Any manufacturer’s recommendations should be taken into account.
An accessory should not be located immediately above an electric oven or hob due to the possibility of people reaching over suffering burns or the flexible cable of connected equipment being damaged.

Regulation number(s):

• 522.2.1

Q1.53 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

Q1.54 How close can an accessory and/or consumer unit or distribution board be installed to a sink or to a wash basin to protect from splashing?

BS 7671 does not specify a minimum height or horizontal distance.  However, Regulation 512.2.1, relating to external influences, requires that equipment shall be of a design appropriate to the situation in which it is to be used or its mode of installation shall take account of the conditions likely to be encountered.

Regulation 522.3.1 requires a wiring system to be selected and erected in such a way that no damage is caused by condensation or by ingress of water whilst being installed, used or maintained.

When installing standard accessories, good practice would be to install them at least 300 mm horizontally from the extremity of the sink bowl (excluding drainer) or wash basin opening. 

For commercial premises, the same principle applies.  However, the designer may consider it appropriate, due to the increased risk of splashing or the use of water jets, to install equipment that has a degree of protection of at least IPX4 or IPX5 respectively, as appropriate.

If an accessory is encountered closer to a sink than this during a periodic inspection, engineering judgement will need to be applied to determine whether this is safe. An accessory so located for a considerable time that had not suffered any perceptible water ingress or damage would not warrant a classification code or comment on the Electrical Installation Condition Report.

General guidance is to avoid positioning a consumer unit immediately above or alongside a sink.

Regulation number(s):

• 512.2.1
• 522.3.1

Q1.55 Where a cable is to be concealed in a sloping surface that could be considered to be either a wall or a ceiling (such as in a loft conversion), should the requirements of Regulation 522.6.201 and 522.6.204, relating to a cable installed under a floor or above a ceiling, be applied, or should the requirements of Regulations 522.6.202 to 522.6.204, relating to a cable concealed in a wall or partition, be applied?

It is indeterminate which of the above regulations should be applied where the sloping surface might reasonably be considered to be either a wall or a ceiling. Nevertheless, it is still necessary to comply with the fundamental requirements of BS 7671 for protection of a wiring system against impact, which are given in Regulations 522.6.1 and 522.6.2.

One way of meeting these fundamental requirements in the case of a sloping surface that could be either a ceiling or a wall is to design the part of the installation concerned to meet the requirements of Regulation 522.6.201 and 522.6.204 and the requirements of Regulations 522.6.202 to 522.6.204.

Regulation number(s):

• 522.6.201
• 522.6.202
• 522.6.203
• 522.6.204

Q1.56 When an electrical appliance such as a boiler or electric towel rail is to be installed in a bathroom where there is no supplementary bonding, and the consumer unit has rewireable fuses and no RCD protection, how can the installer comply with BS 7671?

If an existing circuit of a location containing a bath or shower is extended, at least the extended part of the existing circuit must be provided with RCD protection. Supplementary bonding in a bathroom or shower room must be provided unless all the requirements in BS 7671 for the omission of supplementary bonding are met.

Regulation number(s):

• 701.411.3.3
• 701.415.2

Q1.57 I have been asked to extend an existing circuit that has no additional protection by RCD using flush wiring at a depth of less than 50 mm without mechanical protection. What should I do to comply with BS 7671?

The preferred option is to provide RCD protection for the circuit at the origin as this gives an improvement in safety for the whole circuit.

Alternatively, an RCD protected, switched, fused 13 A connection unit could be added directly adjacent to the existing outlet from which the extension is being taken.

Regulation number(s):

• 522.6.202 to 522.6.204

Q1.58 Can I carry out an alteration or addition to an existing installation that has inadequate earthing and/or bonding arrangements?

Any alteration or addition to an existing installation must comply with the current edition of BS 7671 (including any amendments). This requires any earthing and bonding arrangements upon which the alteration or addition relies for safety to be adequate. Adequate earthing or bonding is not required where the alteration or addition does not use this as part of the protective measure, e.g. double or reinforced insulation. See also Q1.76 and Q1.77.

 

Regulation number(s):

132.16

411.3.1.1

644.1.2

Q.1.59 Under what circumstances can additional protection by RCD be omitted for low voltage cables concealed in a wall or partition?

Additional protection by RCD is a requirement for low voltage cables concealed in a wall at a depth less than 50 mm from the surface of a wall or partition, or concealed at any depth in a partition the internal construction of which contains metallic parts.

RCD protection for low voltage cables so installed in a wall or partition may only be omitted where the cables:

• Incorporate an earthed metallic covering which meets the requirements of BS 7671 to be a protective conductor, or
• Are installed in earthed conduit, trunking or ducting which meets the requirements of BS 7671 to be a protective conductor, or
• Are provided with mechanical protection sufficient to prevent damage of the cable from fixings such as nails and screws. 

Regulation number(s): 

• 522.6.202
• 522.6.203
• 522.6.204

Q1.60 When changing a consumer unit, do I need to provide RCDs for all circuits required to have additional protection, such as socket-outlets, bathroom circuits and cable concealed in walls and partitions?

Yes. There should be more than one RCD, and the circuits should be divided between them in order to minimize the likelihood and consequences of tripping.

Regulation number(s):

• 314.1

Q1.61 If an existing socket-outlet not having additional protection by RCD needs to be replaced, does such additional protection need to be provided for the replacement socket?

No. Such maintenance or repair work would not be classified as an alteration or addition.

Regulation number(s):

• 411.3.3

Q1.62 I need to replace a length of damaged cable in a circuit that is not RCD-protected. Do I have to provide such protection for the repaired circuit?

No. Such repair work would not be classified as an alteration or addition.

Regulation number(s):

For guidance on what constitutes an alteration or addition see note to definition for Minor Works in Part 2 of BS 7671.

Q1.63 If I replace an existing electric shower, do I now have to provide RCD protection for it?

No, unless RCD protection is recommended by the manufacturer’s installation instructions or a new circuit is required (to provide for increased load, for example).

In cases where the existing consumer unit is of a type that will permit the replacement of an existing circuit-breaker by an RCBO of appropriate type and rating for the circuit in question, the installer may wish to explain the benefits of improved safety provided by carrying out such a, relatively speaking, simple upgrade.

Regulation number(s): 

• 134.1.1
• 510.3

Q1.64 When installing a non-electrical radiator in an existing bathroom, does it need to be supplementary bonded?

Supplementary bonding would be required for any new extraneous-conductive-part installed in a bathroom or shower room unless all the other requirements of Regulation 701.415.2 have been met.

Regulation number(s):

• 701.415.2

Q1.65 In what circumstances can additional protection by RCD for socket-outlets of rating not exceeding 32 A be omitted?

Where socket-outlets are in areas liable to be used by persons of capability BA1 (Ordinary), BA3 (Disabled) or children (BA2, BA3) or are provided for mobile equipment with a rated current not exceeding 32A for use outdoors, additional protection by RCD must be provided.

In any other circumstances additional protection by an RCD may only be omitted for mission-critical or life-safety purposes where a suitably documented risk assessment produced by the elected duty holder (person having significant control) with the involvement of a skilled person (electrically) determines that it is not necessary.

The specific application of the socket-outlet(s) should be recorded on the risk assessment.

The documented risk assessment must  be appended to the appropriate electrical installation certificate.

Regulation number(s):

411.3.3

Q1.67 When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?

Not necessarily. If the existing 6 mm² bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not require to be upgraded.

Regulation number(s):

• 132.16
• 544.1.1

Q1.68 If a dwelling has an existing consumer unit with an integral main switch and an electric shower is connected by means of a second consumer unit with an integral main switch, is another ‘main switch’ required to isolate both consumer units simultaneously?

Regulation 462.1.201 requires a main linked switch or linked circuit-breaker to be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation.

However, it is permitted for a dwelling to have more than one electrical installation. Regulation 462.1 requires means to be provided to isolate each electrical installation from each supply. Therefore a further ‘main switch’ is not required to isolate both consumer units.

Regulation 537.2.7 requires each device used for isolation to be clearly identified by position or durable marking to indicate the installation it isolates.

Regulation number(s):

462.1

462.1.201

537.2.7

Q1.69 When carrying out an alteration or addition to an existing installation protected by a voltage-operated earth-leakage circuit-breaker, can that device be used to provide electric shock protection for the new work?

No. As the new work must comply with BS 7671, fault protection must be provided by an overcurrent device or RCD, and additional protection, where required (such as for socket-outlets or cables concealed in walls), must be provided by a 30 mA RCD.

Q1.70 If I replace a distribution board which feeds a number of sub-distribution boards, am I responsible for testing the outgoing circuits of the sub-distribution boards?

No.

Q1.71 If we reposition a pull switch in a location containing a bath or shower, would the circuit need to be RCD-protected?

Yes, because the work would be more than a like-for-like replacement.

Regulation number(s):

• 701.411.3.3

Q1.72 Is BS 8436 cable resistant to damage by rodents?

No, not without additional mechanical protection.

Q1.73 What should I do if a consumer unit I have been asked to replace is in a relatively inaccessible position?

You should make your customer aware of the issues relating to accessibility, including the need to test RCDs at quarterly intervals, to enable the customer to make an informed decision about the position of the replacement consumer unit.

Regulation number(s):

132.12

513.1

Q1.74 A number of installations are to be combined into one premises resulting in the installation having more than one supply from the distribution network, each with its own main earthing terminal. The installation will have simultaneously-accessible exposed-conductive-parts and extraneous-conductive-parts. Is it necessary to connect all of the main earthing terminals together?

All accessible exposed-conductive-parts and extraneous-conductive-parts are required to be connected to the same earthing system individually, in groups or collectively. This means that the main earthing terminals must be connected together.

Q1.75 Is it permissible to utilise a 4-pole switch with a 2 mm contact separation with series connections to achieve 2-pole 4 mm contact separation for DC isolation?

Yes, but only where the manufacturer's instructions confirm that the switch has been designed for this purpose.

Q1.76 Is it acceptable to add an item of equipment of Class II or all-insulated construction, such as a smoke detector, to an existing lighting circuit not having a protective conductor?

Yes.

Regulation number(s):

• 132.16

Q1.77 Is it acceptable to add an item of equipment of Class II or all-insulated construction, such as a smoke detector, to an installation that has inadequate main protective bonding?

Yes.

Regulation number(s):

• 132.16

Q1.78 I am installing a new circuit in an existing installation where there are exposed-conductive-parts and socket-outlets that are not earthed. Would it be acceptable if I left those exposed-conductive-parts and socket-outlets unearthed and just provide earthing in the new circuit?

No, as this may result in unearthed parts of the existing installation and earthed parts of the new circuit being simultaneously accessible. This is not permitted by Regulation 411.3.1.1.

In any event, whenever an alteration or addition is carried out to an existing installation, it shall be verified that the alteration or addition complies with the Regulations and does not impair the safety of the existing installation.

Regulation number(s): 

• 411.3.1.1
• 641.5

Q1.79 BS 7671 requires socket-outlets rated at up to 32 A to be provided with additional protection by means of a 30 mA RCD. Many socket-outlets in offices may be considered to be subject to this requirement. However, many offices will have computers producing protective conductor current, individually and/or collectively. This accumulated protective conductor current could cause the circuit RCD to operate. Such disruption will not be acceptable to the office users, particularly in banks etc. How can such unwanted tripping be avoided?

Where additional protection by RCD is necessary, unwanted tripping can be avoided by appropriate sub-division of circuits.

Regulation number(s):

• 314.1
• 531.3.2

Q1.80 How do I decide what category and/or type of fire alarm and emergency lighting systems should be provided for a commercial property?

Reference should be to the applicable Building Regulations, BS 5839-1 and BS 5266 which give specific recommendations.

Q1.81 If an RCD is used to achieve automatic disconnection within the prescribed time, is the supplementary bonding called for in 419.2 (ii) still required?

No. An RCD is a valid way of complying with automatic disconnection requirements.

Regulation number(s):

411.3.2.2

411.3.2.3

411.3.2.4

411.4.5

415.2

Q1.82 In a milking parlour, is supplementary bonding required only where livestock can make simultaneous contact with extraneous-conductive parts (such as metallic gate posts and gates) and exposed-conductive-parts?

No. BS 7671 requires all extraneous- and exposed-conductive-parts that can be touched by livestock to be supplementary bonded, whether or not the parts are simultaneously accessible.

Regulation number(s):

• 705.415.2.1

Q1.83 Does a transportable building that is intended to be moved from place to place only infrequently, and which is supplied for example by SWA cable, fall within the scope of Section 717 of BS 7671?

No. Section 717 applies to transportable units that are intended to be moved relatively frequently from place to place and which therefore need to be supplied through flexible cables.

Regulation number(s):

• 717.1

Q1.84 Where automatic disconnection to Regulation 411.3.2.1 cannot be achieved in the prescribed time and supplementary bonding is be provided in accordance with Regulation 415.2, where should the supplementary bonding be located?

At the location of the equipment which cannot be disconnected in the prescribed time. Consideration must be given to disconnection required for reasons other than electric shock, for example, overcurrent protection.

Regulation number(s):

• 411.3.2.5
• 415.2
• 419.3

Q1.85 Where automatic disconnection to Regulation 411.3.2.1 cannot be achieved in the prescribed time and supplementary bonding in accordance with Regulation 415.2 cannot be provided because there are no simultaneously accessible exposed-conductive-parts and extraneous-conductive-parts, (including flooring) is shock protection compliance achieved?

Yes. However, it should be borne in mind that disconnection may be required for reasons other than protection against electric shock.

Regulation number(s):

• 411.3.2.5

Q1.86 Does a single 4 mm² protective conductor in a multicore or flexible cable that does not incorporate additional protection against mechanical damage comply with indent (ii) of Regulation 543.7.1.203 with regard to protection against mechanical damage?

No. The above cable does not meet indent (ii). To comply with indent (iii), duplicate protective conductors would be required. Alternatively, the solutions offered by indent (iv) or (v) could be adopted.

Regulation number(s):

• 543.7.1.203

Q1.87 When the designer of an electrical installation does not intend the steel wire armour of a cable, or a metallic cable management system such as conduit or trunking, to be used as a circuit protective conductor, and a separate protective conductor is employed, does the designer: a) need to verify that in the event of a fault, line to armour or line to cable management system, the associated disconnection time is met? b) need to verify the suitability of the cross-sectional area of the armour or cable management system for the earth fault current?

a) Yes, except where the cable management system is not an exposed-conductive-part. (The steel wire armour of a cable is considered to be an exposed-conductive-part.)

b) No. There is no requirement to calculate or select the cross-sectional area of an exposed-conductive-part unless it intended to be used as a circuit protective conductor.

Regulation number(s):

• 411.3.2.1
• 543.1.1

Q1.88 In a circuit comprising different cable types and/or conductor sizes, for example to allow for volt drop or connection methods, should the distribution board schedule and schedule of circuit details and test results record all the types and sizes of cable used in a circuit?

As a minimum a certificate for initial verification, complete with the Guidance for Recipients shall be provided to the person ordering the work.

  relevant information should be recorded on the appropriate certificate;

• For a MEIWC:    Part 1 Section 5
• For an EIC: Schedule of Test Results – Remarks Column

or, as a separate attachment, to either of the above.

Note: 514.9.1 now contains certain exceptions for diagrams and documentation for domestic premises and similar.

Regulation number(s):

514.9.1

Appendix 6

 

 

 

Q1.89 Does a single 4 mm² internal core, used as a protective conductor in a steel wired armoured (SWA) multicore cable, comply with indent (ii) of Regulation 543.7.1.203 with regard to protection against mechanical damage?

Yes. The armour provides suitable protection against mechanical damage.

Regulation number(s):

• 543.7.1.203 (ii)

Q1.90 In a mobile or transportable unit, what are the conductive parts that need to be bonded to meet Regulation 717.411.3.1.2?

Primarily the chassis. Any structural metal parts connected electrically to the chassis would be effectively bonded. Any structural metal parts not connected electrically to the chassis would be isolated, and would therefore not need to be bonded for reasons of safety.

Regulation number(s):

Part 717

717.411.3.1.2

Q1.91 In a factory, plastic trunking containing socket-outlets is attached to metal tables used to assemble products. Is there a requirement to main bond, supplementary bond or earth these tables?

No. If the tables are not liable to introduce a potential, generally Earth potential, they will not require main bonding.

A dry assembly area would not be considered to be a location of increased shock risk, so there is no requirement for supplementary bonding.

The tables are not items of electrical equipment, so there is no requirement for them to be earthed.

Regulation number(s):

411.3.1.1

411.3.1.2

415.2 Note 4

Q1.92 The run of cables to LED lights supplied by common drivers can be up to 50 m or more, and the cables supplied by the manufacturer are less than 1 mm² copper. Such an arrangement would comply with the manufacturer’s instructions, but does the use of such cables comply with BS 7671 Table 52.3 and Regulation 715.524.201 in terms of cross-sectional area?

Yes. Table 52.3 refers to Section 715 for ELV lighting. Regulation 715.524.201 states that the conductor size is dependent on the load current except where luminaires are suspended from and supported by the conductors, in which case a minimum conductor size of 4mm2 applies.

If the installer decides to use conductors smaller than those permitted by Table 52.3 and Regulation 715.524.201, this would need to be noted as a departure in the Electrical Installation Certificate (Regulation 120.3 refers).

Where a departure is noted in an Electrical Installation Certificate, the designer and/or installer is declaring that the resulting degree of safety of the installation will be not less than that obtained by compliance with the relevant requirements of BS 7671.

ELV cables fitted with plugs and sockets supplied as part of a prefabricated CE-marked LED lighting system (comprising driver, LED lights and interconnecting cables) are assemblies of electrical equipment and are therefore not subject to the minimum cross-sectional area requirements of BS 7671.

Regulation number(s):

113.1

Table 52.3

715.524.201

Q1.93 How can I avoid accidents involving underground services?

Guidance can be found in the Health and Safety Executive’s publication HSG 47 Avoiding danger from underground services, which can be downloaded free of charge from the HSE website.

Q1.94 Is it permissible to connect cables with conductors that have a rated operating temperature of 90 °C to equipment having a maximum rated operating temperature of 70 °C?

Yes, however, Regulation 512.1.5 requires that such equipment shall not be connected to conductors intended to operate at a temperature exceeding 70° C at the equipment in normal service unless:

• the equipment manufacturer has confirmed that the equipment is suitable for such conditions (see Note b of Table 52.1 and Note 3 of Table 4G2A for mineral insulated cables with a sheath operating temperature of 105 °C), or
  
  
• the conductor size is chosen based on the current ratings for 70 °C cables of a similar construction* (see Regulations 526.2, 523.1, 536.4.202 and Table 4A3 Tables 4D1 to 4D5 and 4H1 to 4H4).

 

• Where the current rating of the cable is to be based on 70° C, current – carrying capacities given in Tables 4D1 to 4D5 and 4H1 to 4H4 of Appendix 4 may be used for 90° C thermosetting insulated cables

Regulation number(s):

512.1.5

523.1

526.2

536.4.202

Tables 4D1  to 4D5

Tables 4H1 to 4H4

Q1.95 Where an installation is supplied from a protective neutral bonding (PNB) system, do the minimum sizes of main protective bonding conductors in Table 54.8 of BS 7671 apply?

Protective neutral bonding (PNB) like protective multiple earthing (PME) is a variant of a TN-C-S system, but unlike PME the combined neutral and earth (CNE/PEN) conductor is connected to Earth at one point only.

For a PNB supply, some Distribution Network Operators (DNOs/Distributors) permit the main protective bonding conductor(s) to be sized as for PME; whereas others permit it to be sized as for TN-S.

However, as  advised by the Note above Table 54.8 of BS 7671, designers should always confirm any particular requirements of the relevant local DNO as it may require a larger size of protective bonding conductor to take account of local network conditions.

Regulation number(s):

544.1.1

Table 54.8

Q1.96 From where can guidance be obtained on the use of a PME supply in a location containing a swimming pool or other basin?

Guidance on this can be found in Clause 6.2.5 of Engineering Recommendation G12 Issue 4 (2013) Requirements for the Application of Protective Multiple Earthing to Low Voltage Networks published by Energy Network Association (ENA).

Where it has been decided to use a PME supply, and where the distributor agrees to such use, all the appropriate requirements within Section 702 of BS 7671 must be met.

Q1.97 Within domestic (household) premises, are there any specific requirements to maintain the integrity of the non-combustible enclosure where cables enter or leave a consumer unit having a metallic enclosure?

There is no specific requirement in 421.1.201 for fire-rated cable glands or intumescent sealant to be used for cable entries.

Good workmanship must be applied in particular to limit openings around cables to a minimum. In any case, the requirements of regulation group 416.2 for barriers or enclosures must be met.

Manufacturers’ instructions, if any, should be taken into account.      

Regulation number(s):

134.1.1

421.1.201

Regulation group:

416.2

510.3

Q1.98 With regard to the requirements of Regulation 521.11.201 for wiring in escape routes, what is meant by the term ‘escape route’?

The term ‘escape route’ is defined in Part 2 of BS 7671 as the ‘path to follow for access to a safe area in the event of an emergency’.

Communal corridors and stairways located in industrial and commercial buildings and blocks of flats are examples of escape routes.

In domestic premises examples include passageways and staircases that are the sole means of exiting in an emergency other than escaping from an emergency escape window.

Regulation: Part 2

Q1.98B What is a ‘protected escape route’?

It is defined in Part 2 of BS 7671 as ‘A route enclosed with specified fire-resisting construction designed for escape to a place of safety in the event of an emergency’.

The decision as to what is a  ‘protected escape route’ will be made by a person competent in fire safety engineering design for the particular building.

Regulation number(s):

Part 2

422.1

422.1.1

422.1.2

422.1.3

Appendix 13

Q1.99 Are the requirements for the support of wiring systems given in Regulation 521.10.202 applicable to data and telecommunications installations?

Yes, BS 7671 includes requirements for the fixed wiring for information and communication technology, signalling, control and the like (see indent (vi) of Regulation 110.1.2).

Regulation number(s):

110.1.2

Q1.100 Can a new circuit be taken from an existing consumer unit having all-insulated enclosure?

Yes, so long as within the consumer unit:

• its rating and condition is adequte for the altered circumstances, and
• all existing conductor connections are correctly located in terminals and are tight and secure, and
• there are no signs of overheating, and
• no incorporated equipment is subject to a product recall.

Regulation number(s):

• 132.16
• 526.1

Q1.101 Following on to Q and A 1.100 above, how would this work be described on the EIC?

On the schedule of inspections for new installation work only, item 7.5 should be marked as not applicable (N/A) because it is not a newly installed item of equipment.

Within the ‘Comments on existing installation’ section on the Electrical Installation Certificate a statement should be made that:                                                           

 ‘N/A’ has been recorded against item 7.5 of the schedule of inspections because the addition has been made to a consumer unit that was installed to the requirements of an earlier edition of BS 7671 and has been verified to be adequate for continued use.

Regulation number(s):

• 132.16

Q1.102 What is classed as sufficient in terms of EMC requirements and the information the responsible person must provide?

For basic, non-specialist installations, the installation will meet EMC requirements so long as all installed equipment has UKCA, or CE or CE UKNI marking, applicable to Great Britain (GB) and Northern Ireland (NI) and has been installed in accordance with manufacturers’ instructions, with the instructions being available for reference.

Current and transitional marking requirements for GB and NI can be found at:

https://www.gov.uk/guidance/placing-manufactured-goods-on-the-market-in-great-britain

https://www.gov.uk/guidance/using-the-ukni-marking

Regulation number(s):

512.1.5

Q1.103 At what spacings should wiring systems in escape routes be supported?

Wiring systems, whether cables clipped direct, conduit, trunking or similar should be supported in accordance with the recommendations of the manufacturer.

Regulation number(s):

• 510.3

Q1.104 Can an insulated consumer unit or similar switchgear assembly complying with BS EN 61439-3 be installed in a detached outbuilding of a domestic (household) premises?

Yes, subject to such construction being suitable for ambient environmental conditions such as:

• likelihood of mechanical damage, 
• use of outbuilding for storage of flammable materials such as paint and thinners, or 
• presence of a corrosive atmosphere, such as that found in a swimming pool pump room.

Consideration should also be given to the relative proximity of the outbuilding to the dwelling with respect to the possibility of fire-spread from one structure to the other.

Q1.105 Must all supports for wiring systems be of a type not liable to premature collapse in the event of a fire?

No. Suitable fire-resistant means of support or retention should be provided to prevent wiring systems impeding movement in the event of a fire.

The easiest way of achieving this is for all supports to be of a type unaffected by fire.

Where it is decided to not use only fire resistant supports, this will require careful assessment of the individual circumstances.

Regulation number(s):

• 521.10.202

Q1.106 Does a Consumer Unit with a plastic enclosure and an internal intumescent seal, pad, strip or similar fitted, meet the requirement of Regulation 421.1.201 for an enclosure manufactured from non-combustible material?

No.

Q1.107 Within domestic (household) premises, Does 421.1.201 require the installation of internal or external intumescent materials to a consumer unit?

No. Manufacturers’ instructions, if any, should be taken into account

Q1.108 Regulation 521.10.1 requires that non-sheathed cables can only be installed in trunking if the trunking complies with IPXXD or IP4X. Does trunking bought off the shelf comply with either of these two ratings?

Not necessarily. Manufacturers of trunking systems will be able to advise on making their trunking compliant with Regulation 521.10.1.      

In general, a system assembled properly from compatible parts such as trunking, lids, tees, bends and other accessories will comply, as could a system containing well-made site-fabricated bends although it should be noted that some contracts or specifications will not permit the use of site manufactured bends.

Regulation number(s):

• 416.2.2
• 521.10.1

Q1.109 Do sheathed cables need to be installed in a sleeve where they pass through an external wall?

No.

A sheathed cable can be passed through a suitably sized hole drilled through an external wall without sleeving. Reasonable steps should be taken to ensure that the cable is not damaged during installation.

It is recommended that any such hole is angled downwards so outside hole is lower than that on inside and the space between hole and cable is suitably stopped to prevent moisture penetration.

Regulation number(s):

• 522.3.1
• 522.8.1

Q1.110 When carrying out additions or alterations to an existing electrical installation, what must I do to confirm the adequacy of the distributor / supplier intake equipment?

It is necessary to confirm that the rating and condition of any existing electrical equipment, including that of the distributor / supplier will be adequate for the altered circumstances, such as any increase in electrical loading that the addition/alteration introduces.

It is also necessary to confirm the adequacy, in relation to protection against electric shock, of the earthing and bonding arrangements.

Regulation number(s):

• 132.16 
• 642.2

Q1.111 Is it acceptable to locate the means of connection for a built-in kitchen appliance within the kitchen base unit housing that appliance in such a way that disconnection can only be achieved by first removing the appliance?

BS 7671 does not specifically require the provision of a local means of disconnection to be provided for appliances.

However, many manufacturers of built-in appliances recommend that a means of disconnecting the appliance should be accessible when the product is installed; therefore it is advisable to request any special installation instructions pertinent to their equipment from those supplying such equipment.

Q.1.112 There is a clamp on the sheath of a service cable at the property in which I am about to start work. Is this acceptable?

Yes. Engineering Recommendation G12-3 published by the Energy Networks Association permitted Distribution Network Operators (DNOs) to install BS 951 clamps on the sheath of a cable. G12-4, published in 2013, now permits DNOs to use clamps which comply with EREC C93. So, both BS 951 and other clamps may be encountered on the sheaths of service cables.

On no account should an electrical contractor fit a clamp to the sheath of a service cable.

Q.1.113 What action should an electrician take when they encounter a clamp on service cables to provide the earth connection for an installation forming part of a TN-S system?

Before starting any electrical installation work or when carrying out a periodic inspection of an installation, the electrician must confirm that the earthing facility is sufficient in terms of the requirements of BS 7671.

One way to verify the adequacy, or otherwise, of such a connection is to carry out a measurement of the impedance of that part of the earth fault loop external to the installation (Z_e) at:

• the cable sheath, and
• the clamp.

The two readings obtained should be substantially the same.

Typically, the maximum impedance of that part of the earth fault loop external to the installation (Z_e) is 0.8 Ω. However, due to network conditions this value is sometimes exceeded.

Responsibility for ensuring the safety and effectiveness of this connection rests with the DNO (Regulation 24(1) of the Electricity Supply Quality and Continuity Regulations (ESQCR)). 

Q.1.114 Following on from the question above, what action should be taken if the result obtained from the measurement of the impedance of that part of the earth fault loop external to the installation (Ze) is unsatisfactory?

The electrician should advise the customer to contact the relevant Distribution Network Operator (DNO) and request that the ineffective connection on their equipment is rectified.  The DNO may be able to provide a TN-C-S earth to the property although there may be a charge to do so.

Alternatively, the electrician can offer to convert the system earthing to TT through installation of earth electrodes and any required RCD protection.

On no account should:

• any attempt be made to further tighten, connect, disconnect any such clamp encountered on the sheath of a service cable.
• the contractor attempt to fit a clamp to the sheath of a service cable.

Q.1.115 In relation to indent (ii) of Regulation 421.1.201, does the cabinet or enclosure of a consumer unit or similar switchgear assembly have to be constructed of ferrous metal (steel)?

No. Note 1 of 421.1.201 gives ferrous metal as an example of a non-combustible material. The cabinet or enclosure can be made of other non-combustible materials. However, the installer will need to judge whether such material used will provide adequate protection. Account will also need to be taken of Regulation 132.12 in relation to accessibility.

Regulation number(s):

• 421.1.201 (ii)

Q.1.116 BS 7671 does not state a minimum depth for buried cables. Where a cable is buried in a household garden, what depth of burial would be reasonable?

Buried cables, conduits and ducts shall be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground.

A depth of 0.5m is recommended as sufficient to avoid damage by general gardening.

Where more onerous conditions are present due to, for example,  ground cultivation then greater depths should be used.

All buried cables should be identified with a warning tape or cable covers above the cable.

It is strongly recommended that the route of a buried cable should be identified on a drawing attached to the Electrical Installation Certificate.

Regulation number(s):

• 522.8.10

Q.1.117 Can one multicore cable be used for more than one final circuit?

Yes.

The circuits and also the conductors of each circuit within the multicore cable would need to be suitably identified to permit inspection, testing, repair or alteration.

Whilst it would be permissible for the multiple circuits to share a common CPC such as the armouring of an SWA cable, it would not be permissible to share a neutral.

Where circuits are at different operating voltages, each conductor must be insulated for the highest voltage present.

When considering current carrying capacity, Table 4B5 of BS 7671 contains rating factors for cables having more than four loaded cores.

Regulation(s) 514 group; 521.7; 528.1; Table 4B5.

Q.1.118 Is it acceptable to locate an electrical accessory, such as a socket outlet, directly under a kitchen sink?

Yes.

Where water connection valves serving appliances such as washing machines and dishwashers are present, socket-outlets should be so placed that water from these valves or hoses connected to them is unlikely to affect the socket-outlet or plug during connection or disconnection of the appliances.

Q1.119 Do switch-disconnectors installed as part of a solar PV installation have to be non-combustible or mounted in a non-combustible enclosure to meet Regulation 421.1.201?

No. Regulation 421.1.201 relates to consumer units and similar switchgear assemblies complying with BS EN 61439-3 Low voltage switchgear and controlgear assemblies.  Distribution boards intended to be operated by ordinary persons (DBO). 

Switch-disconnectors (both AC and DC), otherwise known as isolating switches, are designed and manufactured to a different standard -  BS EN 60947-3 Switches, disconnectors, switch-disconnectors and fuse-combination units and therefore are not subject to this requirement unless they are incorporated within a consumer unit or similar controlgear assembly.

This does not preclude the specification or use of switch-disconnectors having non-combustible / metal enclosures.

Regulation number(s):

537.1

Table 537.4

Appendix 1

Q.1.120 Does BS 7671 require the use of capping where electrical cables are to be plastered over?

A. No, however this does not preclude its use. 

Q1.121 Does BS 7671 require protective bonding of the metallic pipework within a building?

A. Protective bonding is only required where the pipework is an extraneous-conductive-part. Such protective bonding should be applied as near as practical to the point of entry of that pipework to the building.

Q 1.122. Where plastic incoming service pipework e.g. gas, water, oil etc. enter a building is protective bonding required?

No.

Regulation number(s):

• 411.3.1.2

Q 1.123. When would it be necessary for main protective bonding to be connected to metallic pipework within a dwelling?

When it is proved to be an extraneous-conductive-part.

Regulation number(s):

• 411.3.1.2

Q 1.124. Does BS 7671 permit a 13 amp BS 1363-4 fused connection unit to supply a detached outbuilding such as a shed or garage from a ring or radial final circuit?

Yes, provided all relevant design criteria is verified as suitable.

Regulation number(s):

• Sections 311, 312, 313, 314 and Appendix 15

Q 1.125. Where automatic disconnection to Regulation 411.3.2.1 cannot be achieved in the prescribed time and supplementary bonding is to be provided in accordance with Regulation 415.2, does the supplementary bonding cross-sectional area or conductance need to comply with the relevant regulation(s) in 544.2?

Yes, the requirements in 544.2 apply to all supplementary bonding conductors.

Regulation number(s):

• 415.2
• 544.2

Q 1.126 For an electrical installation condition report, what is the limiting service life of a BS 3871 circuit-breaker or other equipment to a Standard not currently listed in BS 7671?

It is impossible to give an exact generic figure in terms of recommended service life. This is due to a number of factors.

As an indication as to whether the device is in a satisfactory condition for continued service, it must be manually operated and examined to validate that it is of the correct type and ratings and has no signs of thermal / mechanical damage, arcing or overheating.

Regulation number(s):

• CH 65 - Appendix 6 condition report inspection schedule (4.8, 4.14)
• Electrical Safety First Best Practice Guide 4

Q 1.127 For an electrical installation condition report, what code or comment should be recorded for a BS 3871 circuit-breaker or other equipment to a Standard not currently listed in BS 7671 that has been manually operated and passed the relevant examinations? Does the situation change depending upon the age of the equipment?

Irrespective of the age of the BS 3871 equipment, a code or comment is not required provided there is no deterioration, defect, or non-compliance with the current edition of BS 7671 that may give rise to danger. 

CH 65, Appendix 6 condition report inspection schedule (4.8, 4.14)

Electrical Safety First Best Practice Guide 4

Q1.128 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.

However, it is essential to confirm that the measured value of Z_s is not indicative of a defect, such as a loose connection or an inadequate means of earthing.

Regulation number(s):

411.4.4

411.5.2

 

Q1.129 Are plastic wall plugs an acceptable fixing method for the support of wiring systems to prevent premature collapse?

Yes. Properly selected and installed plastic wall plugs can be used to support cables, wiring systems and the like.

Q1.130 Where split concentric cable complying with either BS 4553 or BS 7870 is run as a sub distribution circuit (sub main) in consumers' premises, must this be recorded as a departure on an electrical certificate, since neither of these standards are included in either Appendix 1 or Appendix 4 of BS 7671?

No.  Appendix 1 includes only those standards which are included in BS 7671 and Appendix 4 is informative not normative.    

Split concentric cable in the LV range complying with either one of two British Standards - BS 4553 and BS 7870 - may be selected, if appropriate to the intended use, without infringing the requirements of BS 7671.      

Split concentric thermoplastic insulated and sheathed cable is listed in Table F4 of IET Guidance Note 1, Selection and Erection as one of the types of cable that can be used for fixed wiring.

Split concentric cables can be used in consumers' premises, provided they comply with the relevant cable standard and are installed in accordance with the requirements of BS 7671.  Some types of terminal and clamping unit are unsuitable for the multiple neutral conductors of split concentric cable.  Consequently, installers must take account of instructions for terminations provided by the manufacturer of the distribution board / consumer unit.  

Regulation number(s):

• 133.1.1
• 510.3
• 511.1

Q1.131 Is there a maximum acceptable value of resistance for verifying the effectiveness of a main protective bonding conductor and do I have to record it on a BS 7671 model form?

No, there is no defined maximum limit of resistance stated within BS 7671. However, there is a requirement to verify continuity by measurement. The measured value need not be recorded.

Regulation number(s):

• 544.1.1
• 643.2.1

Q1.132 Are SRCDs and FCURCDs manufactured to BS 7288 deemed acceptable for providing additional protection for use in AC installations?

Yes.

Note: Devices to BS 7288: 1990 will be of RCD type AC. Devices to BS 7288: 2016 will be of type AC or type A, with the type marked on the product.

Regulation number(s):

531.3.4.1

531.3.4.2

Q1.133 When extending a lighting circuit only protected by an overcurrent protective device, to supply a mains powered smoke alarm in a domestic property, does the requirement of Regulation 411.3.4 mean that a 30 mA RCD is required?

No. Regulation 411.3.4 applies to circuits supplying luminaires. Extending an existing circuit to supply a smoke alarm does not affect the protective measures for the existing circuit. Therefore, RCD protection is not necessary with respect to Regulation 411.3.4.

However, other requirements relating to RCD protection shall be met where necessary e.g. for a cable concealed in a wall at insufficient depth.

 

Regulations:

• 132.16
• 411.3.4
• 522.6.202
• 522.6.203

Q1.134 Is it a BS 7671 requirement that isolating switches or switches for mechanical maintenance provided for showers, extractor fans, cookers etc. must be lockable in the off position?

No, BS 7671 refers to several precautions that could be applied to prevent unintentional or inadvertent closure such as: located within a lockable space or lockable enclosure, padlocking, located adjacent to the associated equipment.

 

Regulation number(s):

• 462.3
• 464.2
• 537.2.4

Q1.135 Can OCPD 2 in Fig 534.5 be omitted, and OCPD 1 used for the SPD short-circuit protection?

OCPD 2 may be omitted where all of the following apply:
• The SPD is in a household or similar installation
• The SPD conforms to BS EN 61643-11
• The SPD manufacturer’s instructions state that OCPD 2 can be omitted, and specify the required OCPD 1 characteristics (typically the cut-out fuse has a rating not exceeding 125 A)

Regulation number(s):
134.1.1
361.1
534.4.5.1
534.4.5.2
534.4.5.3
Fig 534.5

Q1.136 If OCPD 2 is installed, is it a requirement under Regulation 534.4.5.2 to achieve selectivity with OCPD 1?

When OCPD 2 is required according to the SPD manufacturer’s instructions, partial or total selectivity should be verified between OCPD 2 and OCPD 1.

Account should be taken of the SPD and OCPD manufacturer’s instructions.

 

Regulation number(s):

134.1.1

361.1

534.4.5.1

534.4.5.2

534.4.5.3

Fig 534.5

Q1.137 Is it permissible to install electric vehicle charging equipment or other items of electrical equipment/switchgear, within a meter cabinet (the cabinet specifically designed and intended to house distributor supply and metering equipment) at the service position of domestic and similar premises?

Whilst a meter cabinet is owned by, and is the responsibility of, the homeowner, the space within the cupboard is designed for the use of electricity industry apparatus only, and no allowance is made for additional equipment to allow safe access for maintenance or replacement.  For this reason, it is strongly recommended that such items of electrical equipment are not installed within a meter cabinet.

Link to government guidance as below:

Smart metering for domestic new builds: guidance for developers and architects (publishing.service.gov.uk)

Q1.138 Where additional protection is required for a circuit connecting a generating set, e.g. PV generator to the installation, is the RCD required to switch all live conductors, including the neutral conductor?

A: Yes, for reasons as described in Best Practice Guide 3, figure 2: this requirement was originally introduced in BS 7671:2008 17^th Edition.

Regulation number(s):

522.6.202

522.6.203

551.7.1

Q1.139 Does metallic pipework connected to a heat pump, which is located outdoors, require connection to the main earthing terminal (MET) by a main protective bonding conductor at the point of entry to the building?

Only if the metallic pipework is an extraneous-conductive-part.

Part 2 Definitions (extraneous-conductive-part), Regulation 411.3.1.2 and 544.1.2.

Q1.140 Are there any particular requirements for heat pump installations in BS 7671 which preclude the use of a PME earthing facility as the means of earthing for the supply of such equipment?

No.

Q1.141 How can it be determined if a conductive part is an extraneous-conductive-part?

A method of verifying whether a conductive part is an extraneous-conductive-part would be to carry out resistance testing using an insulation resistance tester at 500 V DC, between the MET and the conductive part.

Depending on the safe level of current deemed acceptable, the minimum resistance value where bonding would not be required could be within a range of 6.67 kΩ - 22 kΩ.

The table below gives indicative values depending on example levels of current:

Safe level of current	Where the resistance values are higher than these values then the conductive part need not be considered to be an extraneous-conductive-part
10 mA	22 KΩ
30 mA	6.67 KΩ

 

Note: Other verification methods may be suitable.

Part 2- Definitions, (Extraneous-conductive-part)
Regulations: 411.3.1.2, 643.1

Q1.142 On a photovoltaic system, is a separate DC isolator required (adjacent to the inverter) if there is one already provided on the PV inverter itself?

Yes, a separate DC isolator should be provided, unless the inverter provides DC isolation conforming to Table 537.4 including Note 1.

Note: Where connectors conforming to BS EN 62852:2015+A1:2020 are not utilised in the connection of the inverter, a separate DC isolator shall be provided.

Table 537.4

Regulation: 712.537.2.101