Intermittent trips driving me mad

[silverdiy]

Theres a lot of background to my question but just keeping it short-ish ...
For over a year I've had intermittent trips on the RCD and after a lot of advice/searching decided the most likely cause was a rather old fridge on one of the power rings but not the kitchen socket ring. Since this fridge was only used for keeping drinks cool, I unplugged it in Novenber last year. At the same time I switched off the dishwasher at its swiched spur on the kitchen ring, just to cut down the number of possibilities.
Since then, no more trips in 9 months, so this seemed proof that the old fridge was the culprit.
However, on 11 August we decided to use the dishwasher again (after a lot of visitors) so switched it on at the spur switch, used it but forgot to switch it off agin at the spur.
Three days later, at 2.00 in the morning, RCD trips along with the MCB for the kitchen ring.
The only other appliance on the kitchen ring that was on at that time was the newish fridge in the kitchen - and this has always been on.
So it seems to me that the dishwasher is the likely culprit. Nine months with it isolated at the spur and I have no problem. Three days after its no longer isolated, I have an RCD and MCB trip. Coincidence? I think not.
So what can go wrong with a dishwasher that's switched off at the appliance itself but still getting power supplied to it ??
By the way, it's a Neff which have had a safety issue with fires but my unit is not one of the dodgy batch.

 

[EFLImpudence]

There could be accumulated earth leakage on the dish washer (which would still be contributory when not in use but not isolated) and another appliance which together is enough to trip the RCD.

Heating elements and motors or moisture are the likeliest causes.

 

[securespark]

I'm not a white goods expert, but they can give surprising results.

I went to a house with an intermittent RCD tripping issue and IR tested everything with all appliances disconnected. It was fine. I gave the wiring a clean bill of health and told the customer there must be an issue with an appliance, possibly the fridge. I was back there countless times after the appliance guy swore the fridge was OK after testing it.

It got quite serious and involved my manager but in the end the fridge was the culprit. The appliance guy was so embarrassed, as every time he tested it, it was fine, no sign of any fault, the IR was not low or dipping.

The same could be true of your dishwasher.

An electrician my future parents-in-law knew actually disconnected an earthing conductor from a TN-S installation (IDIOT) because an RCD kept tripping.

In the end, we discovered a fault with the dishwasher element, and because the earth was disconnected, the fault was free to wreak its havoc.

Effectively what happened was the fault caused an arc that cut right through the bottom of the stainless steel dishwasher cavity, in the shape of the element.

Try leaving it disconnected and keep a note of any future tripping.

Then get an appliance guy to look at it. But not the same guy who looked at the fridge!!!

 

[ban-all-sheds]

An electrician my future parents-in-law knew actually disconnected an earthing conductor from a TN-S installation (IDIOT) because an RCD kept tripping.

Careful - mustn't insult people.

 

[securespark]

I'm only going to say a couple of things:

The word is in CAPITALS for a reason. Think about it.

And one final comment: compare my record of throwing insults at people to yours.

 

[viewer]

Come on girls.
To the question: the OP said the MCB had tripped as well as the RCD, so this isn't a simple cumulative leakage. The advice has got to be isolate the dishwasher now. His might not be one of the known "dangerous" batch, but the suggestion is a faulty component. It is for the OP to work out the various costs of repair, replacement or hiring an au pair, but certainly he should consider the machine as unsafe.

 

[bernardgreen]

Is the dishwasher hard wired ( switched off the dishwasher at its swiched spur ) or does it also have a 13 amp plug in a socket. ?

If it has a 13 amp plug then replace the fuse in the plug with a 3 amp fuse ( or 1 amp if you can get one ) and leave it plugged in but do not use it.

If the RCD trips then check the fuse in the dishwasher plug. If that has blown then the dishwasher does have a serious fault.

A 13 amp fuse may not blow before the trip in the MCB operates. A 3 amp fuse is more likely to blow before the MCB trips but that is by no means certain.

Have you pulled the diswasher out to see if there is any damage to it's cable ?

 

[ericmark]

One of the problems with the RCD is neutral - earth faults. These can completely lead one astray as a fault with say a mixer can cause the RCD to trip when a kettle is used.

I am not saying this is the problem in your case but it is often hard to isolate the real problem.

As well as true earth leakage problems some early trips would be activated by spikes. Very common for when I reset one RCD for the other one to trip. Bad connections can cause tripping and it may not even be in your house.

I expect an average of 4 false trips a year some times 4 years without a trip then 4 trips within a month with nothing wrong in the house.

There are good and bad RCD's some will reject spikes better than others and a series of RBCO's are less likely to trip than using just two RCD's for everything like I do and have done for 20 years.

For real faults then first is to test for neutral - earth I am lucky I have a PAT tester so simple plug in and test. The problem is appliance switches often don't switch neutral.

Anything with a temperature switch or timer is a problem. Be it the auto defrost on a freezer or the spin cycle on a washing machine only by opening up the machine can one really test it and that is not what we want to do.

However most homes have at least 2 RCD's so the easy way is extension lead and run suspect items from the other RCD. Yes I know it's a pain but cheaper than getting some one with an insulation tester or PAT tester to check all items and because of the timer problem likely more of a fool proof method any way.

 

[Bluehair]

However most homes have at least 2 RCD's

I am not sure about that looking at the age of the UKs housing stock.

However your suggestion to try a different RCD is a good one. Maybe a plug in RCD?plugged into a non rcd supply of course

 

[lxboy]

I would strongly advise you have a qualified electrician undertake a insulation resistance test on your wiring to identify any potential fault.
And have the appliance Pat tested.

Regards,

lxboy

 

[JohnW2]

I would strongly advise you have a qualified electrician undertake a insulation resistance test on your wiring to identify any potential fault. And have the appliance Pat tested.

I certainly agree that an electrician should look into this. An intermittent fault which causes a (presumably) 32A MCB (as well as an RCD) to operate is clearly quite a serious situation - but I strongly suspect that neither IR testing of the wiring nor 'PATesting' of the appliance would, in themselves, shed much light on the situation. I suspect that more extensive investigation/testing than that will probably be required.

Kind Regards, John

 

[FDJ]

So what can go wrong with a dishwasher that's switched off at the appliance itself but still getting power supplied to it ??

Most likely, its a "delta suppressor" which has failed. These are connected between L, N & E before the appliance switch so sit across the supply even when the device is switched off.
A cheap and easy repair and easy to diagnose with an insulation tester.

 

[JohnW2]

Most likely, its a "delta suppressor" which has failed. These are connected between L, N & E before the appliance switch so sit across the supply even when the device is switched off.

If that suppressor failed comprehensively enough to operate a 32A MCB, wouldn't it be so knackered that the appliance would be inoperative, and such that it would be impossible to reset the MCB without unplugging the DW?

Kind Regards, John

 

[securespark]

I would strongly advise you have a qualified electrician undertake a insulation resistance test on your wiring to identify any potential fault. And have the appliance Pat tested.

I certainly agree that an electrician should look into this. An intermittent fault which causes a (presumably) 32A MCB (as well as an RCD) to operate is clearly quite a serious situation - but I strongly suspect that neither IR testing of the wiring nor 'PATesting' of the appliance would, in themselves, shed much light on the situation. I suspect that more extensive investigation/testing than that will probably be required.

Kind Regards, John

You'd be surprised: I have often found an appliance fault can bypass a 13A BS1362 fuse and trip a BS3871 or EN 60898 instead.

 

[JohnW2]

You'd be surprised: I have often found an appliance fault can bypass a 13A BS1362 fuse and trip a BS3871 or EN 60898 instead.

No, that doesn't surprise me at all - I've often observed, and commented, on such lacks of discrimination myself. My point was that for a 'spontaneous' and intermittent (and presumably 'transient') fault to result in operation of a 32A MCB (whether or not the BS1362 in the plug operated) (which would require a very minimum of 36A fault current) would surely be a very unusual situation, indicative of something being 'seriously awry', wouldn't it?

Kind Regards, JOhn