RCD tripping - nothing plugged in

[LadyJane]

Hi
Came home from work late at night to find no power. The RCD had tripped. Put it back on, all is well. It tripped 5 mins later, put it back on, tripped about 10 mins later. Rang electrician who advised to turn off all circuits, put rcd on and then one by one put fuses on to see which one tripped it. None tripped the RCD, until 20 mins later.
After trial and error it turned out to be the downstairs plugs. I unplugged everything as he asked. 20 minutes later it tripped the rcd so I turned the fuse off to the plugs and went bed.

The electrician on the phone can't come until late this evening and I don't want to ring a random one from phonebook. He said it was odd for the MCB to trip at random times with nothing plugged in. He then asked if I had put any pictures up or had a plumber in, but the answer is no, and I don't really understand why he asked that!!!!
can anyone offer help, or should I just wait.

 

[JohnW2]

The electrician on the phone can't come until late this evening and I don't want to ring a random one from phonebook. He said it was odd for the MCB to trip at random times with nothing plugged in. He then asked if I had put any pictures up or had a plumber in, but the answer is no, and I don't really understand why he asked that!!!! can anyone offer help, or should I just wait.

I presume you mean RCD (per your previous comments), not MCB. I fear you'll probably have to wait, since something 'non-obvious' is clearly going on. Just one question - do you have any 'outside' electrics - lights, switches, sockets etc.? Water/moisture in such things can cause the sort of problems you are experiencing.

BTW, he asked that question because someone may have damaged a buried cable with a nail, screw or drill.

Kind Regards, John.

 

[LadyJane]

Hi
thankkyou John, very quick reply.
The big switch says Crabtree RCCB, is this what is meant by RCD?
I understand where he was going now with his questions. He also asked about outside power,lights etc as it was a very rainy day.But we dont have any.
I'm just concerned as on the phone he was unsure as to what would cause it to trip at random times without further tests , which I assume will mean time and cost. and my friend in work said to come on here and ask the question.

 

[JohnW2]

I'm just concerned as on the phone he was unsure as to what would cause it to trip at random times without further tests , which I assume will mean time and cost.

I fear that's the case - although how much time and cost is impossible to guess. It just depends upon how obscure the cause is. On the oprimistic side, it could be that the cause will be detected and cured very rapidly once a few tests have been done.

Kind Regards, John.

 

[JohnD]

a downstairs socket circuit which trips the RCD even with everything unplugged (not just switched off) might be rodents gnawing underfloor cables, or water getting into something (could include a socket under a window or near a leaky pipe).

Make absolutely sure that all watery appliances such as washing machines and boilers, and also heating appliances or ovens, are unplugged or disconnected (not just switched off) and that sockets hidden behind appliances are not wet or damaged .

If you have lights or sockets in a shed or garage, that might be what's getting wet. Or a porch light. Or an extractor fan.

An intermittent trip like this is one of the more difficult problems to trace.

Sorry.

 

[LadyJane]

Hi,
Thanks for replies, looks like I'll have to wait and see what the electrician finds out.
I have double checked everything is unplugged. The kitchen is seperate so freezer, washing machine etc are all on different circuit.
I'll let you know how he gets on tonight.

 

[martinxxxxxx]

I had one of these last Sunday and it was traced to a SLUG in one of the sockets. Poor thing had fried across the terminals and caused the same problem as you are having.

Just shows it could be almost anything from rats to water to slugs.

Hope he sorts it for you, would be v int to know what caused your problem

 

[JohnW2]

I had one of these last Sunday and it was traced to a SLUG in one of the sockets.

Reminds me of the dead mouse piccie! As a matter of interest, with what IP rating would this socket have complied? I know we have 'Standard Fingers', but I don't think there are any 'Standard Slugs'!!

Kind Regards, John.

 

[LadyJane]

Well, it gets interesting. When electrician arrived the 'MCB' was off, he turned it on and did not trip the RCD. We waited 5 mins, still no trip. Then he pLugged his machine into downstairs socket. First test was 'no trip' and passed. Next two meant to trip it and it did. Put RCD back on, still wouldn't trip on its own.
Then 5 mins later the rcd tripped. It would only reset with the MCB for downstairs off.
So with downstairs off, he removed socket in the dining room. Tested for power, there was none. So he took the red cables out and said he was looking for a ring to split. When he tested the reds, his machine beeped and blew a fuse in the machine. This did not please him, as this meant he could not do any further testing. He had no spare fuse.
He will be back first thing tomorrow morning. Electrician slightly baffled but he says he will not charge until fault is found, then will only charge for fixing fault. He has worked for our family before.
He still reckons there is damage or water leaking somewhere which would explain the time difference in the tripping.
What he didn't know is why it blew a fuse in his tester as the socket had no power when he tested it.

 

[JohnW2]

What he didn't know is why it blew a fuse in his tester as the socket had no power when he tested it.

Hmmmm - it takes electricity to blow a fuse!

I hope he's being careful, and will be very interested to hear what he discovers tomorrow.

Kind Regards, John.

 

[bernardgreen]

Is there a rogue connection to next door's electrics ?

Long shot but I have seen it before. Socket on a party wall connected to the socket on the other side of the party wall. ( intentional theft of electricity ) Lighting with a neutral borrowed from the ring main of the flat above ( accidental )

Is there a party wall involved and has maybe by accident the electrics of next door become involved with yours. Have you got a socket accidently wired to a cable of the next door electrical installation. That could explain why there was fuse blowing power on one red wire ( from next door ) when your MCB for that socket was off.

 

[Space cat]

I have double checked everything is unplugged.

Not everything on a ring is 'plugged in'. It's not unusual to have stuff permanently connected through fused connection units (FCUs). Examples: extractor fans, burglar alarms, heating controls, cupboard lights, doorbells, fan assisted radiators. Anything that's fixed could, potentially, be connected this way. Look for anything that only works when the socket MCB is on.

Some FCUs have switches on them - and maybe a light too. Others are un-switched and inconspicuous. Our utility room lights are supplied from an un-switched FCU on the upstairs ring. Isolating something on an un-switched FCU is not a simple matter of pulling the fuse out. That leaves neutral still connected and a neutral-earth short can trip an RCD.

 

[LadyJane]

Hi, thanks for all your replies. This is where we are at the minute. The electrician has said it was the live circuit earth test that must have blown the fuse in his machine. When he turned off mcb and went to do a continuing(?) test on the red cables, his machine wasn't already working. It managed a live/negative test on the socket as that didn't involve his machine putting power through the leads, it was only when he did the other test did he realise the machine was broke as the fuse was blown. sorry if this garble doesn't make sense, but I'm sure the electrician explained it better!!

I said about what Spacecat suggests to the neutral/earth but he said they are connected all the time and doesn't trip, it only trips when the mcb goes on, so it more than likely a live/earth problem. He can't explain why sometimes it will be 5 seconds or 20 minutes from mcb going on to making it trip.
He can't get a new fuse today, so he will start taking off all the sockets tomorrow and will be running continuing tests and mega tests on the cable as he goes.
will keep you all updated, thankyou for showing an interest. luckily we have another seperate downstairs circuit so we are running a few extension leads for the tv etc.

 

[JohnD]

The electrician has said it was the live circuit earth test that must have blown the fuse in his machine.

sounds like he forgot to set it correctly. An easy mistake, everbody does it at least once.

 

[Space cat]

it only trips when the mcb goes on, so it more than likely a live/earth problem.

Fair comment - unless there's a load on the circuit that you don't know about. MCB is on ---> unknown load draws current ---> current returns partly through neutral but also through earth ---> RCD trips. And that short could be in a cable beyond an un-switched FCU, even if its fuse is out.

Idea: If it's a load that comes on at random times, that would explain the random nature of the tripping.

But of course it just as easily could be a live-earth leak anywhere around the circuit. Intermittent faults are an absolute pig to sort out.