Earth Trip keeps cutting out

[Crackle]

Hi
I was wondering if I could get some advice on a problem I am experiencing with my household mains supply cutting off at the earth trip. It is only intermittent but last night it happened 2 times and this morning again 2 times. When it trips out it is often impossible to reset with out first switching off the individual circuit breakers.

I am thinking that the main problem may be a combination of slight leakage on more than one circuit. I suppose they can combine to finally take the 30mA trip out.

Do earth leakage trips fail as they get older?

I carried out some tests today with isolating various circuits to see if it was still difficult to reset the trip.

It seems to be the circuit which feeds amongst other things the supply to the shed up the garden and the fish pond pump, filter and UV filter.
My tests with a multimeter dont show up any faults.

I was thinking of using my isolating transformer on the circuit, with the output earth disconnected from the supply and reconnected to the negative on the output socket. I was also thinking of using a plug in 30mA earth trip on the output of the transformer just in case there was any leakage in any of the pond units.

I was wondering if someone could advise on this arrangement.

Thanks
Mike

[Murphyv310]

You could have slight leakage in the pond pump, try isolating it initially then move to the shed wiring.
How is your shed feed done, buried in conduit pvc cable, armoured cable etcetera,?

[ppppenguin]

More than likely a bit of water in the outdoor cable or a joint in it. You really need a megger to check the insulation, a low voltage test may well not find any problem.

Since it's intermittent it could be a marginal insulation fault or possibly something that gets wetter and dryer from time to time.

An isolating transformer feeding the relevant circuit is a sort of fix but not really recommended as it leaves a dubious and leaky circuit outdoors just waiting to give somebody a nasty shock.

Having a single RCD protecting the whole isntallation is a nuisance. The most recent (17th ed) wiring regs require that the load be split between at least 2 RCDs. Even better is to an RCBO (combined MCB and RCD) for each circuit. Though that's an expensive method.

[Craig]

Nuisance trips of this sort are a PITA. We have returned from holiday twice to find the freezer a mass of food going off. In our case it was a flaky RCD, and replacing it cured the main problem. But when we had major work carried out when we had the kitchen remodeled, the electrical contractor fed new wiring to the fridge and freezer sockets to a separate RCBO circuit, so even if the RCD tripped and took out all the other circuits, the fridge and freezer stayed on.

But if you have leakage somewhere that is triggering the problem - as others said the individual circuits need to be isolated and individually tested. Personally I'd get a qualified electrician in; it might cost a couple of hundred, but you will end up with a certified job done that can be used for insurance purposes.

[ppppenguin]

Having the fridge/freezer on its own circuit is a good idea. An RCBO is ideal for this. It's just about possible, even under 17th ed regs, to run a fridge without an RCD. The wiring routes need to carefully considered (anything buried in a wall must be more than 50mm from surface or in metal conduit) and the socket must be marked that it's for fridge only.

[Terry]

I agree with Jeffrey about using individual RCBOs. When we moved in here, the CU still used rewireable fuses! As we also needed additional sockets in several places, a rewire seemed the obvious solution, although our electrician has checked out the original wiring and retained most of it.

He suggested RCBOs for the critical circuits and, having heard all the horror stories of problems with one RCD, it made good sense.

So now, a few of the circuits, including the lights and Ring Main, are all on an RCD but the fridge is on a separate RCBO as will be the freezer when it comes up from Ilford, the garage and other kitchen sockets.

[ppppenguin]

My own house is still on 15th edition regs. RCDs for the garage and outdoor sockets plus an RCD for my lab bench. Otherwise ordinary MCBs. No need to update.

[boater sam]

If the RCD has persistantly tripped with a full load on I would replace it anyway.
Isolate and megger every circuit, it could be a bit here, a bit more there, adding up.
Pond pump is a good suspect.

Using one RCD foe everything is always a problem waiting to happen.
There was a criminal who used to find houses with an outside socket, trip the mains, which turned off the alarm, and return a few days latter when the batteries had failed to rob the house. Most alarm batteries are not changed frequently enough, they lose charge quite quickly when not being topped up.

[Ed_Dinning]

Hi Mike, don't forget the N/E leakage will also trip an RCD.

Ed

[Murphyv310]

Well so much for RCD's
Made a near fatal mistake when working on a Peavy amp today. I'd run it up on the open mains but pulled the wrong mains lead, leaving the Peavy powered up. Once unscrewed I was pulling the chassis out and had touched the constantly live fuse and chassis. Got a right nasty rattle and a cut thumb. Did my three year old RCD trip?? Did it heck, so there you go one supposed safety device didn't do its job.