RCD trips during the night - possibly during a thunderstorm.
Won't turn back on.
Disconnect and reconnect circuits one by one to find the one responsible. Completely repeatable: turn on the circuit and the RCD trips immediately.
Turn off switches on all the sockets on the responsible circuit. RCD doesn't trip any more.
Turn the sockets back on one by one. RCD still doesn't trip. Now what?
-- Richard
If there's a next time, turn the sockets *off* one by one!
Just to be clear, is that with all the other cicuits fed through that RCD off?
What appliances are connected? Lots of equipment with switched mode power supllies? That's computers, tellies, DVD/PVR, set top boxes, printers, routers, switches, switched mode wall warts, etc).
They may well "leak" quite a lot through their supression components when all powered up together. Switch them on sequentially and you don't get that excessive "leak".
It's just gone again, and this time one switch made a difference: a switch controlling a security light in the garden. Which seems plausible: presumably some damp has got in there. And maybe the order of turning them on is what caused it not to happen before.
Thanks to those who replied.
-- Richard
Could you have some kind of carbonisation? If its in multi sockets only a little bit more leakage probably pushes it over the top when reconnected, but if you ramp up the drain gradually then it holds. One could test this by doing the c gradual power up, then tripping manually. If it reconnects OK Then i don't know, but in my expeerience it is either minor leaks de to carbonisation, some connected device with a leak, or a faulty rcd.
In that order.
All thunddrstorms should do is induce a momentary current into a circuit, that can trip things but they should reset as you say.
Have you got megga? Brian
Can also damage the filter compenents wired directly across the mains inside the appliance. Not kill 'em but enough to ake 'em leak a bit more.
But as the OP has now mentioned an outside light that's were my money is going.
I feel the recent heavy rain might help cause the leakage!
Sounds like a classic case of RCD sensitisation. There is enough leakage on all the circuits its feeding to put it very close to its tripping point - but not quite. At that point even a small disturbance such as a voltage transient or current surge will be enough to trip it. So for example powering on a circuit load of stuff is enough to cause a trip.
Have a read through the following for a plan on tracking down the cause:
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