"Mano" wrote in message
...
OK open to ideas here with this one :-

we have a mcb style mains board (crabtree from memory) which has an RCD
device built in. Normally when when for an example a bulb goes the trip
for that lighting circuit goes bit of a pain but we can live with it.
However yesterday and today has been a nightmare with the main breaker
tripping on average every two hours! No individual circuit goes and
throwing the break brings everything back to normal (apart from having to
reset the times on the cooker microwave stero etc!).

At a loss for any ideas. Nothing has changed regarding load no new devices
etc and its happened day and night so its not something we are manually
turning on or off.

any ideas where to start ?

Switch off individual breakers and see when/ if the problem goes away. After
determining the circuit at fault you can then isolate individual appliances
on that circuit until you isolate one that causes the problem to go away.
You then attend to that appliance. If you can identify an individual circuit
that has problems but no appliance has a problem, then you have wiring/
wiring fitting problems.

If the problem doesn't go away at all using any of the checks above you
then, most probably, have a defective MCB.

I think you may have some confusion between the function of an mcb and that
of an rcd. The mcb will trip if the circuit current exceeds the value quoted
on the mcb, whereas the rcd will trip if the difference in the current
flowing in the live and neutral conductors exceeds a minimal value, normally
30 mA (30 thousandths of an ampere). The two devices are intended to protect
you against rather different circuit faults and may well be protecting you
against fire at this very moment.

Call in a qualified electrician and get it sorted! Don't do any nasty
desperate bodges!