RCD trip again! Ideas?

[Bear]

About 6 months ago I had a re-occuring RCD trip issue - after some faffing around I replaced the kettle (even though it work fine in other sockets) and all was well. Today I plugged the iron into a different socket to usual and ...bang. RCD tripped. Reset the trip and tried a second time - same result. So plugged the iron into an extension lead and powered it from my sons bedroom instead. No problems.

So I'm guessing it's not a faulty iron. And the iron doesn't have a particular problem with earth leakage as it worked in another socket (and incidentally always worked in it's usual socket). And no, I wasn't running a small generator or drawing an unusual amount of electricity when it happened - although interestingly the sandwich toaster always uses the socket where the iron tripped and has never had a problem - it also runs at a max of 2kw, like the iron - only difference I suppose is one uses/creates water/steam - could this be significant?

Next steps - swap the socket with one on the other side of the kitchen

- see if the problem disappears (unless someone has a better idea)?

[A.Lee]

Is this a MCB that is tripping, or a main RCD? If the MCB, then they do go faulty and trip too quickly. I have changed loads before that either tripped all the time, or would not turn on. They are only £7 - 10, so may be worthwhile changing it - don't be tempted to get a higher ampage rated breaker, get the same size. Aaln.

[Bear]

Thanks for the advice but it's the main RCD tripping. I'm about to try some earth leakage tests using all I have (a digital voltmeter). I'm starting to suspect either the socket is faulty. The only other alternative I can think of is that the wiring is faulty - which is a less pleasant thought. Interestingly, once I'd finished ironing using my sons socket and an extension lead, I tried plugging it back into the offending socket and all worked well! I even tried aggravating it by switching it on/off several times and pushing it to the max setting (2kw). No problems.

I'm now trying to recreate the conditions of the fault again by letting the iron cool, and then plugging it in from cold.

[Dave Liquorice]

Is this the same socket that the "faulty" kettle was being used on?

[Peter Parry]

It is almost certainly a neutral to earth fault or a faulty RCD. Given the time and intermittent nature I suggest a neutral/earth short circuit is more likely. Note that this fault need not be on the circuit where actually plugging something in causes the trip, it could be anywhere in the house on any circuit.

[Fredxx]

It may still be a faulty iron if other items work on the upstairs ring. I had one which was intermittent from leaking water, which was fine when hot and temperamental when cold.

Only other thing I can think of is that the earth is floating on your upstairs circuit?

[Fredxx]

Correction

[terry]

If RCDs work same as GFCIs (North American protected outlets etc.) it sounds like it 'might' be some sort of current unbalance live/neutral. Dodgy iron; maybe leakage to earth/ground?

[John Rumm]

May as well post the usual:

[NT]

Your train of thinking strikes me as confused. The second thing I'd do is test all appliances using a multimeter, or preferably if you've got access to one, a megger. The first would be read the article John linked to.

NT

[John Rumm]

Yup pretty much, although we tend to use them in the breaker box to protect complete circuits rather than just individual outlets.

See:

the background...

Could be, or leakage elsewhere sensitising the RCD so that it is close to tripping. Then it only takes a transient (like the stat in the iron cutting in or out) aided by a few mains inlet filters (as found is loads of kit these days) to push it over the edge .

[Bear]

Thanks for the posts - I read the relevant wiki's on this topic previously when I had the same issue with a faulty kettle (thanks for the links all the same). If the iron were faulty (which would logically be the first thought), why does it work on other sockets without a problem?

Yes Dave, it is the same socket the faulty kettle was being used on (a twin standard household unit). I'm going to test the earth to neutral resistance tonight on both the iron, and the twin sockets. And I'll try a known good one also.

Fredxx - we are in a bungalow. Pete - I guess the fault could be anywhere on the circuit, but would it not be more logical to either be the plug socket itself, or the wiring from the ring to the socket?

[NT]

More often the problem is with an appliance rather than the fixed wiring. The nature of earth leakage is such that inconsistent behaviour is very common. The socket could only be considered to make a difference is you get a repeatable behaviour difference between the two sockets. Random chance is more likely.

NT

[Bear]

Thanks for the idea. Never had a problem with the iron and the other sockets though - it's always this one particular one - which also happened to be the one where the old kettle played up. Hence I'm considering the repeatable behaviour difference you mention

[Dave Liquorice]

That points very strongly to a problem with that socket rather than the kit being plugged into it. But has been said there are many interrelated reasons for nuisance trips of RCDs.

IIRC this socket is in a kitchen. I think I'd just replace the socket and (hopefully) be done with it but the curious side would want to know what the fault really is. It might be obvious when you remove it from the wall, dead creature, build up of crud, damp, loose terminal.

[Dave Plowman (News)]

Remember RCDs add any leakage until they get to their limit then trip. Could be you've got other things leaking slightly and the iron just tips it over. Moving it to a different socket might just change things slightly.