DIY Doctor UK DIY Forums

The power circuit on my 3 month old consumer unit trips the RCD every evening, usually between 6-00pm and 11-00pm, always once, sometimes 2 or 3 times. No MCBs ever trip.
All photo-sensative lights have been unplugged and items like the central heating and garage have been transferred to the non-RCD side of the unit.
During daylight hours all the many domestic appliances in many sockets operate at full blast and the RCD never trips.
Has anyone any suggestions, no matter how bizzare....I am becoming desperate!
Thankyou in anticipation of your kind help to a suffering mortal!
DavidO

faulty rcd, replace asap!!!!!

Computers, video recorders, New TVs, and many other house hold items now use a voltage reducing device called a switch mode power supply. These have large capacitors in them to store the power. If any of these are unplugged and plugged back in it can produce a spike which can trip the earth leakage trip. So step one make sure everything is plugged in properly look at where the lead plugs into appliance as well as wall side.

A neutral earth fault is next on list. While there is a low power draw the earth and neutral are nearly the same voltage so a fault may not be enough to trip the earth leakage but as the power used increases the differential between neutral and earth increases and now the item can trip the earth leakage. So can be something which is used all day causing problem not just stuff used at night. Meters are really only way to find this.

If that fails you may have something small with wrong neutral supply or using earth instead of neutral. Clock or neon but unlikely. Could be supplied from lights but return though sockets. Again really needs a meter to find.

Of course the last the Earth leakage unit may be faulty. And the meters don't always work here. I have found many times a trip which passed all tests but when changed with another which also passed all tests we had no more problems.

I hope that gives some pointers

Thanks so much for your prompt reply 'stecook'
In fact the RCD was relaced some weeks ago, to no avail I'm sorry to say.
But thanks again.

Many thanks to you also 'ericmark'. The bit about new TVs was especially useful as my wife tripped the RCD today when she unplugged and replugged our slimline tv to share multiplug with her hair-dryer! The tv display took several seconds to disappear; now I know why.
I'll re-check all the connections as you advise. I'd be most grateful to know what 'meters' you refer to in your reply. It may be I need to buy one or two such items and the all look reasonably priced in the 'Tools' section. Your guidance would be appreciated, then I promise to leave you alone!
Thanks again, David O.

An Earth leakage test meter is used six times. There are two test half cycles and both are tested so each test is done twice. First the current is set to half the value on the earth leakage trip which should not trip the earth leakage trip. Next current test set to tripping value it should trip. And then time set at 5 times tripping value it should trip in 40ms. The meters are around the £300 mark and because to the traceable records problems are not normally hired. Electricians will normally buy as one of three meters a special ohm meter using 500 volt on Meg Ohm range and set current on ohm range and An Earth Loop Impedance meter combined with Prospective short circuit current. Normally between £750 and £1000 for the lot. I would not consider them as reasonable price I borrow my sons. Multi-sockets can cause earth leakage problems as many are not good quality. Any multi-sockets with filters built in are specially suspect they do have limited life.

Hi dave, make sure Neutrals are on same half of board as lives for each circuit, also as ERICMARK says if N-E fault switching off lights ect. won't cure it could be outside light full of water, still give prob even if switched off, circuits will need insulation tests if visual check comes up blank, with experienced fault finding sparky 'driving' it,
regards SPARX