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

Switch off individual breakers and see when/ if the problem goes away. [...]

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

Not necessarily true. A neutral-earth short anywhere in the
installation (or an appliance) could cause the reported symptoms.
Isolating individual final circuits would not help in this case, unless
the OP has double-pole MCBs (unlikely).

I think you may have some confusion between the function of an mcb and that
of an rcd.

So do you, judging by your reply above. Anyway it's fairly rare for
RCDs to become defective and when they do fail they tend to become
insensitive, or won't trip at all, rather then becoming over-sensitive.

A faulty appliance is the most likely cause. Start with washing
machine, dishwasher, fridge & freezer (esp. if frost-free type),
immersion heater, toaster. Unplug or isolate these completely, such
that the neutral is disconnected too.

--
Andy