The 17th Edition of the Wiring Regulations (BS 7671: 2008) will introduce a number of new requirements for the installation of RCDs, therefore it is timely to look at the requirements within the 17th Edition for verification of RCDs.
The continuing effectiveness of these RCDs needs to be confirmed periodically. This article discusses the verification required where RCDs are used to provide automatic disconnection of supply in the event of a fault and additional protection. It should be stated at this point that the 17th Edition does not introduce any significant changes in the requirements for the testing of RCDs even where they are installed to provide automatic disconnection in the event of a fault.
Use of RCDs to achieve automatic disconnection in case of a fault 411.3.2.1 requires (in most cases) that a protective device shall interrupt the supply to a line conductor of a circuit or equipment in the event of a fault of negligible impedance between said line conductor and an exposedconductive- part or a protective conductor for the circuit or equipment within the appropriate required disconnection time. A disconnection time of 5 seconds for distribution equipment and final circuits of rating exceeding 32A is permitted by 411.3.2.3. Similarly, a disconnection time of 1 second for distribution equipment and final circuits of rating exceeding 32 A is permitted by 411.3.2.4.
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Originally published in Wiring Matters, Spring Edition 2008, written by Jon Elliott