Alterations and additions in domestic and similar premises

Q2.1

Do socket-outlets added to an existing installation in domestic premises have to be RCD-protected?
Where socket-outlets are added to an existing circuit that is not already RCD-protected, either the circuit will need to have RCD protection added, or the new socket-outlets must incorporate RCD protection (except for a socket-outlet designated for a particular item of equipment, such as a freezer). However, refer also to Q3 and A3.
Regulation number(s)
- 411.3.3
Q2.2

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 the 17th Edition?
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 the 17th Edition for the omission of supplementary bonding are met.
Regulation number(s)
- 701.411.3.3
- 701.415.2
Q2.3

A socket-outlet is to be added to an existing circuit. The work is not being carried out in a special location and the existing circuit has no RCD protection. The new socket-outlet is to be flush mounted 150 mm horizontally from an existing socket-outlet, and connected with wiring concealed in the wall. What is reasonably expected for the installer to do to comply with the 17th Edition?
A socket-outlet that is added to an existing circuit will need to have RCD protection (except for a socket-outlet designated for a particular item of equipment, such as a freezer).

In addition, if the wiring that is used to extend the existing circuit is concealed in the wall, then at least the extended part of the existing circuit will need to be suitably protected (by RCD or other means).
Regulation number(s)
- 411.3.3
- 522.6.101 to 522.6.103
Q2.4

A switched, fused 13 A connection unit is to be added to an existing circuit. The work is not being carried out in a special location and the existing circuit has no RCD protection. The incoming services are bonded and the new switched fused connection unit is to be flush mounted 150 mm horizontally from an existing socket, and connected with wiring concealed in the wall. What is the reasonably expected for the installer to do to comply with the 17th Edition?
The connection unit does not require additional protection by RCD, though at least the extended part of the existing circuit will need to be suitably protected (by RCD or other means).
Regulation number(s)
- 522.6.101 to 522.6.103
Q2.5

Can I carry out an alteration or addition to an existing installation that has inadequate earthing and/or bonding arrangements?
No. 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.
Regulation number(s)
- 132.16
- 633.2
- 411.3.1.1
Q2.6

How can I avoid providing RCD protection for a new socket-outlet intended to supply a particular item of equipment for use indoors, such as a fridge or freezer, when cables concealed in a wall or partition, and socket-outlets, are generally required to be RCD protected?
Cables concealed in a wall or partition are not required to be RCD protected if they are installed in accordance with Regulation 522.6.101 (i), (ii), (iii) or (iv), or Regulation 522.6.103 (i), (ii), (iii) or (iv), as applicable. This includes cables having an earthed metallic covering or earthed metallic enclosure meeting the specified requirements.

The socket-outlet would need to be specifically labelled or otherwise suitably identified for connection of the particular item of equipment
Regulation number(s)
- 522.6.101
- 522.6.103
- 411.3.3
Q2.7

When changing a consumer unit, do I need to provide RCDs for all circuits required by the 17th Edition 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
Q2.8

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
Q2.9

I need to replace a length of damaged cable in a circuit that is not RCD-protected. The 17th Edition would require a new circuit following the same route to have additional protection by means of an RCD. 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)
- 411.3.3
Q2.10

If I replace an existing electric shower, do I now have to provide RCD protection for it?
No, unless RCD protection is required by the manufacturer’s installation instructions, or a new circuit is required (to provide for increased load, for example).
Regulation number(s)
- 134.1.1
- 510.3
Q2.11

When installing a non-electrical radiator in an existing bathroom, does the 17th Edition require it 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
Q2.12

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
Q2.13

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 537.1.4 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. Therefore a further ‘main switch’ is not required to isolate both consumer units.

Regulation 537.2.2.6 requires each device used for isolation to be clearly identified by position or durable marking to indicate the installation it isolates.
Regulation number(s)
- 537.1.4
Q2.14

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.
Q2.15

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.
Q2.16

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
Q2.17

Is BS 8436 cable resistant to damage by rodents?

No, not without additional mechanical protection.
Q2.18

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)
- 513.1
- 132.12
Q2.19

How should the like-for-like replacement of a circuit-breaker be recorded?

It is recommended that such maintenance work be recorded on a Minor Works Certificate, job sheet, invoice or similar.
Q2.20

Is it acceptable to issue a Minor Electrical Installation Works Certificate for the replacement of a single protective device where an Electrical Installation Condition Report has identified departures such as:

a. 'lack of additional protection by RCD', or

b. 'maximum loop impedance values exceeded'

and the remedial work would invovle:

a. replacing a circuit-breaker with an RCBO, or

b. replacing a Type C circuit-breaker with a Type B, or replacing a 10 A circuit-breaker with a 6 A device

Yes. A Minor Works Certificate makes provision for all the required test results for the remedial work described, and requires a competent person to certify that the work does not impair the safety of the existing installation and that the design, construction and inspection and testing of the work complies with BS 7671.
Q2.21

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.
Q2.22

Is it permissable to utilise a 4-pole switch with a 2 mm contact separation with series connections to achieve 2-pole 4 mm contact separation for d.c. isolation?

Yes, but only where the manufacturer's instructions confirm that the switch has been designed for this purpose.
Q2.23

What form of certificate should be issued for the addition of a voltage optimisation unit to an existing electrical installation?
Fitting a voltage optimisation unit might affect the existing installation in a number of ways that could have a detrimental effect on its safety, including the introduction of additional impedance (potentially affecting the automatic disconnection of circuits) and disturbance of connections possibly introducing a fault or potential fault.

In order to demonstrate that the safety of the installation has not been impaired, it will be necessary to perform some inspection and testing of those circuits supplied via the unit.

An Electrical Installation Certificate would be needed to record the results of this inspection and testing. It is unlikely that the necessary details could be adequately recorded on a standard Minor Electrical Installation Works Certificate.
Regulation number(s)
- 633.1
Q2.24

With reference to the preceding question, what inspection and testing is necessary when a voltage optimisation unit is installed in an existing installation?
It is necessary to carry out inspection and testing sufficient to demonstrate that the safety of the existing installation has not been impaired, including:
- inspection of connections
- continuity of protective conductors
- insulation resistance
- polarity
- earth fault loop impedance.
Regulation number(s)
- 633.1