ASK THE EXPERTS
From the helpline We continue with our series of answers to some of the more frequently asked questions put to the NICEIC Technical Helpline
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I want to make an addition to an existing installation that is protected by a voltageoperated earth-leakage circuit-breaker (VOELCB). Can I use this device to provide fault protection to the addition?
No. An addition or alteration to an existing installation must be carried out to meet the current requirements of BS 7671. VOELCBs have not been recognized by the IEE Wiring Regulations as devices for fault protection since January 1985. Consequently, they have never been recognized for that purpose by BS 7671 (which was first issued in 1992). Just as for a new installation, fault protection for an addition or alteration to an existing installation must be by means of either an overcurrent protective device or an RCD (Regulations 411.4.4 (TN system) and 411.5.2 (TT system) refer). Where the addition or alteration forms part of a TT system, Regulation 411.5.2 indicates that an RCD is preferred. This is usually necessary in any case because the earth fault loop impedance (Zs) in a TT system is too high to allow an overcurrent protective device to be used for fault protection.
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I’m repositioning a ceilingmounted switch in a location containing a bath or shower. Do I have to provide additional protection by an RCD?
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Yes. Repositioning an accessory constitutes an alteration to the installation. The work must therefore be carried out to meet the current requirements of BS 7671. As the switch is in a location containing a bath or shower, the circuit connected to the switch must be provided with additional protection by RCD having the characteristics specified in Regulation 415.1.1 (IΔn not exceeding 30 mA, and operating time not exceeding 40 ms at 5 IΔn), as required by Regulation 701.411.3.3.
NICEIC Connections Summer 2010 43