Q & A of the Day - Is this RCBO OK for a domestic lighting circuit?

Published: 27 January 2011 Category: Q&A

Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, about the suitability of an RCBO to protect a domestic lighting circuit, is answered by ABB:

Question: Knowing the advantages of using Type C devices, can one use a 6A BS EN 61009-1 Type C RCBO for a domestic lighting circuit that has a 1mm circuit protective conductor (CPC)?

I have read, in the On-Site Guide, page 104 - Table 2D, that the minimum protective conductor size recommended for such Type C devices is 1.5/2.5mm, depending on fault level.

Answer: When using RCBOs you should use the guidance relating to RCDs rather than the MCB part when considering protective conductor sizing. This is because it is the RCD that will act on faults to earth at a much lower current (30mA typically) compared with the 60A from the C curve MCB characteristic.

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