In article ,
spamlet wrote:
The main RCD in our consumer unit seems to be very much on a 'hair
trigger' and cuts out regularly, causing mayhem to pc users and dvd
recorders!

We thought at first it was just when the heater in the washer/drier
kicked in, but closer observation shows that it trips in various
combinations of heating element devices like
kettle/toaster/cooker/washer, tending most to cut out if two of these
happen to be on at once.

The current imbalance that the RCD trips out at is additive - sounds like
you have several small leakages which are very common with certain types
of heating elements. Hence the common use of split load units that allow
things like cookers and immersion heaters to be fed from the non RCD
protected side.

Also light circuit RCD always trips when a light bulb goes, but main
also trips if the light's earth is touched when removing lamp holders
even when the lighting RCD is 'off'?

An RCD works by measuring tiny current imbalance between neutral and
earth. Short neutral to earth with the circuit switched off and you get a
tiny current flow between those but not in the line. So the RCD trips.

The consumer unit was fitted by a competent electrician and the problem
was not immediately apparent after the fitting.

Could be the 'leakage' of some appliances have increased since then.

Do the RCDs wear out?
How can they be tested?

There are devices available for this purpose. You might be able to hire
one. But probably cheaper to just replace it on spec. But I doubt it's
actually faulty.

Cheers for any tips,

S

--
*Never miss a good chance to shut up.*

Dave Plowman London SW
To e-mail, change noise into sound.