Q & A of the Day - Do ELCBs give the same protection as RCDs?

Question: Please could you clarify whether a 30mA ELCB provides the same protection as a 30mA RCD. Could you also clarify as to whether it complies with the regulations with regard to shock protection in domestic dwellings.

Answer: An ELCB works by detecting a voltage to earth, and in the event that this voltage exceeds its setting (50V), it will operate. An RCD looks to detect a current (say 30mA).

The difficulty with ELCBs is that they require an earth to operate effectively and that any fault currents are driven through the device and to earth. As installations have been modified over the years, we often find that the earth paths have been paralleled with that of the ELCB - rendering the device ineffective.

The other consideration that should be given to keeping the ELCB in commission is whether it can be effectively tested. There are very few contractors who would still have the necessary test equipment.

Note that BS7671: 2008 does not recognise ELCBs as a means of providing additional protection.

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