RCD tripped during thunderstorm...

[tony sayer]

In article , Lobster writes

You might not have done, but a surge induced many miles away?....

[wanderer]

Err, I presume it is a modern RCD and not an old voltage operated trip? Those were very prone to spurious tripping because of induced voltages which can occur during thunderstorms.

If it's a fairly modern RCD then your guess is a good as anybody else's. The principle is simple, what goes up the live must come back on the neutral otherwise it thinks there's a fault, although I believe newer models also have electronic as distinct from electro-mechanical detection, so that could have responded to an induced surge on the mains.

[Lobster]

...at 3am last night. I can't believe it's a coincidence, but given that (AFAIK!) we didn't get struck by lightning, why would that have happened? David

[tarquinlinbin]

Yes i have one of these also. Its the older type with the grey rocker switch and the little yellow push to test button above it. All the fuse carriers also have circuit breakers. I'm 100% sure there is no defect in the house as it can go for months if not a year without tripping ,then it might trip say twice in one week,then its ok for another long period. I've jammed something under it now to hold it in,not sure if it will though or whether the switch design will still cut the power,,its a damn nuisance,I'll get round to changing the consumer unit one of these days...

joe

Change the 900 to 670 in the return email address to reply

[Andrew Gabriel]

If it's an old voltage operated earth leakage circuit breaker (which you can tell because it will have two quite separate earth connections to it), then this is typical behaviour. It will trip when someone else's earth leakage leaks back into your earth through the ground, including lightning strikes nearby.

Yes -- circuit breakers of all types are still required to trip even when the toggle is held in the closed position. Often they even have provision for locking them 'on' -- this doesn't stop them tripping, but prevents them being reset other than by the keyholder.

[Smudger]

Same thing. You're being pedantic.

Yes it does make a difference. This is a basic scientific/mathematic principle. If you are looking for a needle in a haystack, better that the haystack is the size of a house brick, than the size of a house.

Capacitors are to A.C. what resistors are to D.C.

If you have a capacitor betwen live and earth there will be a continuous current flowing in the capacitor. An RCD will see this as a fault current.

If you have a capacitor between neutral and earth there will most likely still be a (albeit smaller) continuous current flowing in the capacitor, unless the capacitor is so close to the neutral/earth bonding point as to have no useful effect anyway. An RCD will see this as a fault current as well.

Interestingly, the two fault currents will cancel each other out, but as the neutral-earth current will be smaller than the live-earth current, the net result is that the "sensitivity" of the RCD is increased.

Many years experience. Not to mention the fact that the Wiring Regulations have whole rafts of special regulations for bathrooms, swimming pools, etc where you have to take special precautions because water and electrcity make a dangerous combination.

Anyway, I was talking about nuisance tripping, not blown elements in heating appliances, which are almost always going to trip the RCD before the MCB on an earth fault, due to the very fast rise time of a short-circuit fault to earth. Nuisance tripping is where a little water gets between a live contact and earth and introduces a fault current sufficient to trip an RCD. This is often because you spill water when you're filling the iron or you know that you can do four loads of washing one after the other with no problems, but on the fifth, theres a fifity-fifty chance that your RCD will trip when the washing machine goes to its spin cycle and is then fine after you reset the RCD.

Smudger