Is an ELCB as effective as an RCD?

Put simply, no, well not today anyway. The difficulty with ELCB’s (Earth Leakage Circuit Breakers) is that they require an earth to operate effectively. Current operated ELCB’s do exist but for the purpose of this topic we are dealing with the BS 842 Voltage Operated type.

An ELCB works by detecting a voltage to earth, and in the event that this voltage exceeds its setting of 50V, then it will operate. The difference with an RCD is that it is designed to detect current, commonly 30mA.

As installations have been modified over the years, with the addition of supplementary bonding, it is often the case that parallel earth paths are in place in the installation, meaning that not enough voltage will arrive at the ELCB, rendering it useless.

Another consideration is that BS 7671 no longer recognises such devices, there are no test parameters, and I would imagine very few electricians would posses the necessary test equipment for such devices today.

On a final note, my personal advice would be to replace them with a suitably rated RCD should you ‘still’ have one in your installation.

A typical example of a domestic type ELCB is pictured below.