The main switch on my RCD trips without any obvious reason. Here is the basic background.
It usually happens between 9-10am.
It usually happens Mon-Fri and on the odd Saturday but rarely on a Sunday.
More often than not, it is while we are at work so the only things that are plugged in are Clock/Radio, Oven, fridge, water boiler and electric heating. We have had all of these tested and there is no fault.
Nothing is on a timer so nothing to do with why it is so time specific.
We will usually get a pattern, for example: One trip between 9-10am every week day and possibly a Saturday but no sunday. This will repeat for usualy a fortnight and then it stops happening, sometimes for a couple of months. Then it starts again every day as before.
Sometimes (rarely) we get them at about 9-10 at night but hardly ever.
Usually you can just switch the power back on again but recently from time to time when you flick the switch back on it trips immediately and.
Various electricians have checked all appliances, sockets etc and no fault found. They say it is our supplier at fault.
Scottish Power have visited a couple of times and found no fault. They also fitted a recorder for 2 weeks and it showed nothing up even although we had trips while the recorder was fitted.
The story goes on and on but these are the basics. Does anyone have any advice? Many thanks.

David J, June 2008

power has gone on kitchen plug sockets. how can i repair them please?

jace, November 2010

second Afterthought...

Here's my theory - All of the devices in your house are working fine (will not trip RCD) but two of them when operating simultaneously achieve enough leakage (added together) to trip the RCD.

As the RCD mainly trips out when you are not there, the two devices must be either timer controlled or switched by a thermostat. The CH bolier and associated components - Fan, Zone Valve, Pump, Igniter - will be doing their thing when you are away from home. One or even two of them may be contributing to the fault.

Other appliances that "cycle" on their own are firdges and freezers.

If the fault first appeared soon after a change in one of these areas the nature of the change may be a guide to the solution. If the fault has just materialised without an associated change then the cause may be a deteriorating component.

I am aware that electrolytic capacitors tend to fail over time especially in a warm or hot environment like inside your boiler enclosure - there are several electrolytic capacitors in your CH controls (guessing now) and the cause (one or both) may be there.

You have two devices with high leakage that when operating together trip your RCD. One of them is probably associated with your water boiler, which presumably is left on while you're at work.

A control board for a CH boiler costs over £100 + fitting etc. A set of electrolytic capacitors to replace those on the control board are about £1.50. See...
http://kaijaks.co.uk/blog/nick/2008/02/10/dodgy-old-boiler

Richard Buxton, September 2008

Afterthought - Your central heating controls - they must be on a timer and often have week-day settings and week-end settings. Try turning the system off completely before going to work. See what happens.

This never-on-a-sunday fault suggests that some kind of clock timer might be doing it.

Richard Buxton, September 2008

As far as I know an RCD works by comparing the current in the live circuit with the current in the neutral circuit - they should be the same and if they're not the assumption is that the "missing" current is running to earth due to a fault - or through your body because you touched a live wire.

Now workmen digging up the sewers are hardly likely to alter the current between live and neutral so if I were you I would try to eliminate the problem. Trip the breaker for the downstairs lights before setting off to work. If the main rcd still trips out then it's nothing to do with the lights. Do the same for the upstairs lights. Then the upstairs power. When you come to test the downstairs power you may have to run extension cables from an upstairs socket to the fridge/freezer.

If the RCD still trips after all these checks the problem is likely to be the RCD itself or the fridge/freezer. Ask a neighbour for some spare power on a long cable to eliminate the fridge/freezer.

Bizarre.

Richard Buxton, September 2008

If the feezer is not a frost free it will not trip your electrics at the same time each night because it will NOT have a defrost element and a defrost timer, as it clearly won't need one, and therefore won't trip your electric due to it being open circuit.

Simon, July 2008

Hi, Thanks for your reply. We do have a fridge freezer but it too has been checked by an engineer and no fault found. Aparently a fridge freezer that is frost free can cause trips because it defrosts 2/3 times a day but ours is no frost free.
MORE INFO:
Scottish Power told us that the probable cause was that if there were any local works in the area, they were probably tapping into the grid which in turn caused a change in the electricity getting to our house thus causing a trip. I was dubious about this but after a relatively long spell without any trips we started getting lots of trips. It just so happened that at the bottom of our street they were digging and laying new sewage pipes. We got trips several times a day while that work was going on and when the work was finished, we got no more trips and have had none since. Co-incedence??. While the work was still going on I went and asked the workers if they tap into the grid and they said no. They said that years ago they used to do that but they aren't allowed to do it anymore and they just work off generators.

I take your point about unpluggin stuff and process of elimination and that would work if we were getting trips every single day but we can go a couple of months without anything happening. So if I unplug my fridge freezer and after a week I don't get a trip it doesn't necessarily mean that the firdge freezer is at fault because i might not have had a trip anyway.

David J, June 2008

YOUR WRONG,SOMETHING IS ON A TIMER JUST NOT ONE THATS DESIGNED TO HAVE ONE,THE TIMEING IS TOO SPECIFIC.MY GUESS WOULD BE A FREEZER OR FRIDGE GRADUALLY LOOSING TEMP GIVEN HOUSE CONDITIONS TAKEING THE SAME AMMOUNT OF TIME EACH NIGHT AND TRIPPING ON AND OUT AS IT WERE.U DONT MENTION FREEZER ,NOT IN THE GARAGE IS IT?ANYWAY,PROCESS OF ELIMINATION NEEDED.SYSTEMATICALY UNPLUG /DISCONNECT EACH ITEM IN TURN AND WAIT AND SEE.START WITH FREEZER/FRIDGE.DISCONNECTED FOR 2-3 WEEKS ,NO TRIP?AND U FOUND SOURCE.AND SO ON.OR A FULL SYSTEM TEST BY A FULLY QUALIFIED SPARK WITH THE RIGHT TEST EQUIPMENT.SAID EQUIPMENT IS NOT CHEAP SO MANY SPARKS DONT HAVE IT,THOSE THAT DO,CHARGE ACCORDINGLY

CAINE, June 2008