AL_n wrote:
Andy Burns wrote in
o.uk:

AL_n wrote:

I was sitting here at my desk and the whole upstairs lighting went
out. The circuit breaker had flipped. When I tried to un-flip it,
I saw a spark and it wouldn't flip back, so I conclude the short
is still present.

MCB or RCD?

No alterations have been made to the wiring for several weeks
here, so I can't imagine what might have happened. I don't have
rats in the loft.

Try turning all lights off (or reversing them if they're 2-way or
3-way) and resetting the breaker, turn lights back one-by-one until
it trips again, might narrow it down, unless the problem is isn't
in a switched part of the circuit.


Thanks to you all, for the helpful suggestions. This is strange: I
switched all the lighs off and then flipped the circuit breaker. It
flipped back to the "on" position.

I then turned all the lights on, one by one, expecting one of them to
cause the short again. None of them did! Now all the lights are
working.

What does this mean? It makes no sense to me!


How long is a piece of string?

Maybe the MCB is "tired" and will not switch on when under load? It is not
uncommon.

--
Adam