I found a cool piece of old equipment. It's a fault voltage circuit interruptor intended to detect ground faults. It's got 2 ground connections, 1 for the incoming ground (auxiliary ground) and 1 for the load ground. If there was a voltage between load ground and auxiliary ground exceeding 50V it tripped. It's a 10x10x10cm box, still wired to a long piece of old NYM cable with the colors black, black, blue, grey and red. Auxiliary ground seems to be a long green wire.

That sounds like the old British voltage-operated ELCB (Earth-Leakage Circuit Breaker), commonly used as the ground fault protection in rural areas in the past ( U.K. Power Systems , diagram #4).

There are still plenty of these in service in this area.

Ragner,
These units are still in use over here too.
But our units have an arbitary value of trip @ 25VAC.
Only used in areas, where the basics of the MEN supply can't be met, with respect to Fault currents (Earth resistance/Neutral Return).

[This message has been edited by Trumpy (edited 10-25-2003).]

These devices used to be the norm across large area of rural England, before PME was extended and before the current-operated ELCB became common-place.

They were required to trip at 50V maximum, but many actually trip well below that threshold. I've seen a few that will trip out on under 10V.