Electric sockets tripping - mystery! Need help finding solution

Bear · 2009-06-25T07:04:55+00:00

Brief description of problem.Electric sockets only are tripping randomly - happened four timessince moving into our new property on 22/5/09. The first time was twodays after moving in, when barely anything was plugged in. The housewas rewired a couple of years ago and the previous occupants statethey had a similar problem, but it only happened to them a couple oftimes in the 2 1/2 years they were there. The most recent trip was at1am this morning. When it trips, only the electrical sockets in thehouse are knocked out.In locating the fault, I'm making some assumptions: chiefly that ifall of the sockets are turned off (ie. no device is consuming power),its unlikely that anything could trip the RCB. With that in mind, theonly devices consuming power at 1am in the morning are fridge, freezerand combi boiler all of which work on timers/thermostats. Therefore,one of these devices (or the RCB itself) must be at fault?The kettle was originally suspect - on two of the four occasions, ithad not long boiled when the trip occurred. I tested this two nightsago by boiling a full kettle load of water (twice) and then pouring itaway. Tripped both times a few minutes after boiling when the kettlewas off its base. Tried plugging the kettle into the living roomsockets instead - tripped. Replaced kettle. At 1am this morninghowever when it tripped, the kettle hadn't been used for severalhours.Is it possible the RCB is a fault? I can leave the fridge and freezerdoors open, combi boiler running and it doesn't trip so could it be afault with one of these causing a power spike when it's timer/thermostat kicks in? Or is the RCB too sensitive?Please help!

Jun 25, 2009 23 Replies

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Bear 17 years ago

I have checked around 1/2 the sockets in the kitchen but will check the remaining ones this weekend. Yes it is the same side of the CU that trips every time - only the sockets and cooker hood appear to be protected by the RCB. As for substitution I'm not entirely certain what you mean.

The trip can be reset first time after a trip, but last night I switched off the MCBs and then the RCB and unplugged all appliances. Then I switched on the RCB and MCBs. No problem until I started to plug in devices. As more were plugged in the RCB tripped (I couldn't isolate it down to either a device or socket). Resetting the trip wasn't always possible first time - some times I had to wait 10 seconds or more before it would reset.

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Dave Plowman (News) 17 years ago

Have you got an ordinary DVM? If so try measuring the resistance between earth pin and neutral, earth pin and line on all the suspect appliances. Obviously with them unplugged - but switched on if they have a switch on them. And report the results. Not as good as using an insulation tester - but can often show a fault.

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Bear 17 years ago

=A0 London SW

Excellent idea. I do have a DVM - will try this upon returning home this evening.

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John Rumm 17 years ago

If you feel comfortable working in the CU, then you can also test for E N shorts in the circuit that way as well. With everything disconnected (i.e. unplugged) from the circuit, disconnect all wires of both ends of the ring circuit, and measure resistance (with the meter on its highest range) between the various ends. You should be able to verify that there is no shorts between any conductor. You can also verify that you have ring continuity between both ends of each conductor while you are at it (low ohms range). If you can gustimate the circuit length you can compare the results with:

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