Tuesday, 26 January 2010

When is the installation of RCD protection required?

17th edition regulations - circuits requiring RCD protection

The following three items have been affected in terms of RCD requirements by the changes in the 17th edition regulations, these are

1. Socket outlets
2. Cables buried in walls
3. Locations containing baths and showers

Socket outlets are affected by the regulation 411.3.3 which states, in general terms, that all socket outlets up to 20A must have RCD protection and that sockets up to 32A which may be used for outside use must also be RCD protected. The above two items are only required when the outlet in question is to be used by ‘ordinary persons’ i.e. home owners, office workers, cleaners, ect.

The requirements for the installation of RCD protection shown above exceptions may be made where, the use of socket outlets is supervised by ‘skilled’ or ‘instructed’ persons or if the socket outlet is suitability identified or labelled for a particular item of equipment.

All cables buried in walls now require RCD protection assuming none of the following items have been met

1. The buried cable incorporates an earthed metal covering which is suitable as a protective conductor i.e. SWA cabling.
2. The cable is fully enclosed in an earthed metallic conduit which is suitable as a protective conductor.
3. The cable is fully enclosed in an earthed metallic trunking which is suitable as a protective conductor.
4. The cable being protected against damage by penetration by nails or screws. NOTE: this requires the cable to be buried to a depth of at least 50mm in all directions.
5. Be installed in a safe zone.

This is very similar to the sixteenth edition regulations the normal course of action would have been to install the cable in a safe zone, the fifth point, but the 17th edition regulations implements the following stipulation

Where the use of the installation is not supervised by ‘skilled’ or ‘instructed’ person regulation 522.6.7 applies, this states that RCD protection not exceeding 30mA is required.

Overall these regulations require that RCD protection will be required on all domestic socket outlets using thermoplastic cabling, and that RCD protection will also be required in many commercial situations. Below is a selection of pictorial examples of RCD protection requirements

Sourced from: Hagar

In locations containing a bath or a shower, section 701, the requirements for RCD protections have also been changed. Regulation 701.411.3.3 states that all circuits within this area will require RCD protection not exceeding 30mA. This includes fans, showers, lighting, electrical heating devices, ect.

Further more to this 13A socket outlets are now acceptable, provided the outlet is at least 3m from the boundary of zone one.

Within the sixteenth edition regulations required; local supplementary bonding be provided connecting together all exposed and extraneous conductive parts in the (bathroom) zones. This is now not required assuming all of the following items are met

1. All final circuits in the area comply with the automatic disconnection requirements of regulation 411.3.2
2. All circuits are RCD protected by regulation 701.411.3.3
3. All extraneous-conductive parts of the location are effectively connected to the protective equipotential bonding according to regulation 411.3.1.2

As well as the three above conditions RCD protection is also to be recommended for any outside installation. It may also have to be considered for a cooker circuit containing a socket outlet by the regulations mentioned above (it is a commonly forgotten outlet).

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