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 EDQ3 and EDA3.

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.

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).

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).

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. Any exposed-conductive-parts of the new work must not be simultaneously accessible with exposed-conductive-parts of the existing installation that are not connected to the same earthing system.

With the increased requirement for circuits in domestic premises to be RCD-protected, it may be necessary for the smoke detector to be connected to an RCD-protected circuit, which may not be acceptable to the client. How could this issue be addressed without surface wiring?

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.

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.

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.

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).

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.

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.

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.

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.