Comsumer unit RCD trips on non-RCD protected circuit activity




I've got an 8/9 yr old bungalow and a split consumer unit where (only) the
ring main and garage circuit breakers are protected by a 30ma/100A RCD trip

Today, this trip started going at almost any opportunity: unplugging and
resetting didn't help much as any random device may or may not cause the
switch to trip, and sometimes it took a minute before it went. Once it
tripped when I dropped a 4 way extension block that had no devices connected
to it.

I borrowed a PAT tester to check for leakage and plugged it into the cooker
socket as that is not protected by the RCD, but there wasn't much (only found
0.1mA from one device and after checking all bar a couple of devices the rest
were solidly 0.0mA). When I plugged a hair dryer into the PAT unit and ran it
up on full power the RCD tripped again. This doesn't fill me with confidence
as the consumer unit has a split live rail and the RCD is 'downstream' from
the cooker circuit breaker - I don't think it was something else switching on
on the protected ring as the same set of appliances didn't trip it out for
five minutes afterwards.

The general consensus I've got offline so far is that my wiring is stuffed.
I'm having the loft converted at the moment but the new rings have not yet been
connected to the consumer unit, and there has been no-one doing any work for
over three weeks (that's another rant, but serves me right for not DIY, I
suppose :) I've asked for the electrician doing the work to return, but not
heard back from him so far, so I'm looking for advice on tracking things down
a bit.

I will test the remaining devices for leakage (UPSes, which kicked in fine
when the RCD tripped, so I think they're ok) but after that the best advice
I've had is to remove every device from the ring main and turn it off, then
remove all the socket fronts and check the tightness of the wiring, followed
by plugging things back one at a time. The wiring check seems fine, but as
it's a random selection of devices and never just one that causes the problem,
I don't know how putting them back individually might help.

Does anyone have experience of tracking down stuff like this ? Is it worth
turning off the consumer unit and doing the N1-N2, L1-L2 tests mentioned in
the FAQ ?

Thanks in advance,



Andrew Gabriel

You've probably got an earth-neutral short somewhere or such like. These can
cause weird trips even of different circuits. You should do a full periodic
inspection, which should hopefully find which circuit is at fault, which
could be completely different from what you are expecting.

To do the tests you need a proper continuity insulation tester. A 6 quid
multimeter from Maplins will NOT suffice.
Not for a full inspection, but it might still find a neutral-earth

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