DIYbanter - View Single Post - Bathroom switch

Pete Verdon

wrote:

Just tie one of the transformer LV outputs to earth.
If mains meets that side of the LV supply, the fuse/mcb will trip.
If mains meets the other side of the LV circuit, the transformer
secondary will be low enough resistance to allow overcurrent, and
hopefully blow the fuse or trip the breaker, simultaneously frying the
relay.
You cant earth both of course

Um - what transformer?

Presumably the same would apply with the battery though?

I'd wonder about the current-carrying capacity of the wiring on that
side, but I guess it would last long enough to trip an RCD.

Pete