Emergency RCD replacement

ScottishGasMan · 14 Feb 2020

Hey guys.

Rcd at my folks place keeps nuisance tripping, I've isolated the mcbs one st a time and it still seems to sporadically go, can be every couple hours or every couple

Can you test the earth leakage through an rcd with a standard multimeter?

At a guess I think the rcd has just given up, for the sake of keeping them with the lights and heating on over night as they dont keep well, would any rcds from the likes of screwfix fit that board as a temp fix or to even just disprove the current one?

EFLImpudence · 14 Feb 2020

ScottishGasMan said:
Rcd at my folks place keeps nuisance tripping, I've isolated the mcbs one st a time and it still seems to sporadically go, can be every couple hours or every couple

Switching off MCBs is unlikely to help. You need to disconnect the neutral conductor as well.

Can you test the earth leakage through an rcd with a standard multimeter?

No. You need an earth-leakage clamp meter - one that measures milliamps.

There is no earth connection on RCDs they measure the imbalance between Line and Neutral which, if there is one, indicates current flowing to earth elsewhere - anywhere.

At a guess I think the rcd has just given up,

Whilst that is possible, it is more likely that it is doing its job.

bernardgreen · 14 Feb 2020

Switching OFF the MCB for a circuit does NOT isolate the Neutral for that circuit, hence a Neutral to Earth fault on that circuit will trip the RCD if there is any load on any other circuit.

ScottishGasMan · 14 Feb 2020

Ahh, an electrician advised me that method of isolating one MCb at a time years ago for finding the faulty circuit which had worked in past scenarios when I've been trying to prove/disprove boilers in the past, never knew it could still trip even with zero load on the live side.

I only suspected RCd as it must be at least 30 years old and so far has tripped when turning on the boiler, the outside lights, the oven, the kettle and the computer, at various times, I know we could have something leaking 28ma and it's just needing that extra bump to trip it, but then the next time we turn that item on, or all at once it's fine.

Will go look out my clamp meter but fairly certain it doesnt go down to ma.

AndyPRK · 14 Feb 2020

Rcd is probably ok

You best off turn off and disconnecting the N for non essential circuits on the left
And by process of elimination see if that helped

AndyPRK · 14 Feb 2020

Also in plug washing machines, kettles etc. Anything that is wet

ScottishGasMan · 14 Feb 2020

Not realising that it could trip even with out live loads I've went round the house unplugging everything,

Oven/kettle/washingmachine etc all unplugged it was still tripping anything between 2minutes and half an hour, with fridge unplugged it hasn't yet tripped, so plugging everything else back in to see.

If it does look like it's the fridge that's the issue, would there be anything wrong/stupid if I were to make up an extension lead to plug it into, that o could run the earth cable of the extension through the current side of the multimeter to see what the draw is on it?

Had initially assumed one of the boiler pumps as thsts normally what I see causing it, but that's all ruled out, but fridge compressor could be just as likely,

EFLImpudence · 14 Feb 2020

Do you have a socket on your cooker switch?

endecotp · 14 Feb 2020

ScottishGasMan said:
If it does look like it's the fridge that's the issue, would there be anything wrong/stupid if I were to make up an extension lead to plug it into, that o could run the earth cable of the extension through the current side of the multimeter to see what the draw is on it?

Earth leakage doesn’t have to go through the earth wire; it can go through e.g. the feet of the fridge into the ground.

ScottishGasMan · 14 Feb 2020

EFLImpudence said:
Do you have a socket on your cooker switch?

They dont have a cooker switch as I've just learned tonight, its gas hob and electric oven is just plugged into a socket in kitchen.

ScottishGasMan · 14 Feb 2020

endecotp said:
Earth leakage doesn’t have to go through the earth wire; it can go through e.g. the feet of the fridge into the ground.

Fair point, but its got plastic feet and on a wooden floor, could it pass through them to ground?

DetlefSchmitz · 14 Feb 2020

Wouldn't myself expect the leakage to be to anywhere but the earth wire. The principle of the measurement is not bad, but the danger is that without the meter connected the fridge would not be earthed. So no-one is likely to recommend you do it as it goes against all the H&S rules drummed into people.

JohnD · 14 Feb 2020

I once (and I think this is rare) had a fridge that had collected a lot of defrost water in the collection dish (which is round the back on top of the motor, so waste heat helps it evaporate). When I pulled the fridge out the water jolted onto electrical parts beneath (and the motor starter burned out). So it is worth looking at the back of the fridge in case it is water related. It can also be related to rodent damage to cables. Rodents are more common in a kitchen.

As AndyPRK says, earth leakage faults are predominantly on watery appliance, such as kettles, immersion heaters, washing machines, central heating boilers and pumps, electric showers, outdoor lights.

I see the consumer unit has a circuit for a cooker on the non-rcd side. If you can find where this comes out, you can plug the fridge into it. Use a garden-tool type RCD adaptor if you can find one.

Are you sure there are no outdoor circuits? Especially if it trips during or after rain?

RCBOs are one way of isolating circuits when nuisance tripping occurs. I don't know if they are still available to fit that model of Hager CU, the RCD style looks quite old.

flameport · 14 Feb 2020

Realistically, you won't be locating this problem without the proper test equipment.

ScottishGasMan · 14 Feb 2020

Assuming somone did take the earth off the fridge and measured between it and the socket with a multimeter (fluke 115)

A max reading of 0.022A and when monitoring normally it would flash between 0.021 and 0.000 every second or so, that would be a lot for any one appliance to have going down the earth wouldn't it?

Funnily enough talking about that, the freezer has had issues with icing up constantly over last 6 months, so water near compressor wouldn't be an unbelievable suggestion.

It's at least 15 years old so doesnt owe them anything, I'm just glad the heating and lights are on for the night now as they dont keep well at the best of times and have colds/flu symptoms at the moment so thanks everyone for the advice

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Emergency RCD replacement

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