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!

OK, you say "main" RCD... how many do you have?

Could I suggest you have a read through of:

http://wiki.diyfaq.org.uk/index.php?title=RCD

and check the nomenclature to make sure we are not talking at cross
purposes.

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.

This could indicate that you have a faulty heater element in one or more
of these devices. Alternatively you may just have too many devices /
circuits protected by the device, and hence it is normally very close to
its trip threshold.

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'?

Do you mean MCB here? If so that is not unusual - especially with mains
halogen bulbs. In some cases replacing the MCB with a "Type C" MCB
(normal ones are type B) can reduce this problem.

http://wiki.diyfaq.org.uk/index.php?title=MCB

If you really do mean the RCD trips on a bulb failure then that is again
an indication that the leakage current is nominally right on the trip
threshold, and even the minuscule current imbalances that can result
from the effects of surges and spikes on the supply are enough to push
it over the edge.

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

Do the RCDs wear out?

They can fail, but it is not common.

How can they be tested?

Using a RCD tester is the easiest and most reliable way (especially
ensuring that they are tripping fast enough). However there are other
methods described in the RCD article above. See the section on nuisance
trips.


--
Cheers,

John.

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