RCD tripping

[Tim]

we have had huge problems wit our RCD tripping in the house on our farm for no reason. We live on a farm and we have a 3 phase supply comming into a shed in a main consumer unit. it then goes of the the separate buildings. The main buildings like the house and the workshop have a the 3 phases and small buildings only have 1 or 2. The house and workshop then have their own consumer units with 3 phase RCD's in them. Everything is on the RCD's even the lights (this did once save me when changing a light bulb).

The house RCD started tripping about 2 months ago so recently we got an electrician in. He leakage tested everwhere and had floorboards up and all the socket faces off. We have been quoted £200ish for a new RCD device but today we noticed that when you use motorized equipment in the workshop it trips off in the house. (the workshop is all working fine and trips off when tested).

You name it really, electric drills, pressure washer, angle grinder, compressor.

If we have our fridge, freezer and oven off it trips out less.

What do you recon?

Thanks Tim Fish

[Tony Williams]

This is a long post, because it was a very long (and baffling) diagnostic process.

The symptoms sound similar to an RCD-tripping we had a few months ago, reported in this newsgroup, and with some useful advice given.

Chaos here at that time, builders working inside and out.

The tripping seemed initially to coincide with the replacement of the incoming supply cable. Got them back in, got it tested, no faults found.

Then it seemed that the trip happened when certain appliances were used. Megger'd all appliances, and even went to the bother of making a device to measure the L-N difference current when appliances were powered up. No perp found.

Finally realised that the RCD trip was *load-related*. When there was a certain load on the house, then any extra surge current would cause a trip..... didn't matter what appliance, Hoover, Henry, fridge motor, oven element, etc.

Finally (finally!) twigged that we probably had an E-N short somewhere, where our low Neutral voltage was not enough by itself to cause a trip, but was enough to sensitise the RCD.

Sure enough, an ohmeter measurement in consumer unit showed that there was an E-N short. Lifted off every Earth off the busbar and found it was on the kitchen ringmain (somewhere).

A series of low-ohm measurements located the 13A socket that was nearest the short. And (at last!) located a (new) nail head that was also connected to E or N, 4ft above the socket and some distance off to one side.

Pulled the nail, all probs went away.

[Colin Wilson]

Have you measured the volt drop when the stuff with motors start up ?

It could be that triggering a trip...

[Tim]

Yeah this is what ours is like

if there is a large voltage drop farm?

[Lurch]

Is that where volt drop is grown? ..

SJW A.C.S. Ltd.

[Tim]

god knows it seems to have lost the end of my message

i th if there is a sharp voltage drop what can we do about it? would the electricity company pay for out electrician if it is there fault?

thanks Tim Fish

[Lurch]

If you're referring to the incoming supply voltage fluctuating then it's best to contacy REC to come out and monitor the supply. I'm sure I don't need to tell you how difficult it is getting money out of commodity suppliers! ..

SJW A.C.S. Ltd.

[Colin Wilson]

Back to what might be a sensible question - what area of a country are you in ?

(just in case its something I might be able to refer onwards and upwards)

[tony sayer]

Seems like that's the time you want to connect it all to a car battery and see where the smoke comes from;-)....

[Tony Williams]

Almost as desperate/daft as perched on a ladder with an ohmeter, one lead plugged into Neutral, and the other probing along a line of nail heads.

The symptoms are so similar that I think the OP could well have an E-N short (or leakage) somewhere.

[Tim]

Thats what im thinking but would the electrician not have picked that up? He was here for nearly 3 days (at a cost of about £700) and he basically traced all the wiring in the whole house. Surely he wouldnt have missed a E-N short. He plugged some funnny machine in at the consumer unit...

Tim

[Lurch]

Add the word 'intermittent'. Can take weeks to find. ..

SJW A.C.S. Ltd.

[nick smith]

Could it be the trip itself gone faulty ? Try replacing the suspected item with another and see if the problem moves with it...

We had similar intermittent problems, and they turned out to be a corroding washing machine heater element, a dying freezer, and the (still going) toaster which allows the bread which curls when cooking to touch the elements. None of these happened before I fitted the RCDs, so the wife suggested I remove them ( :-) ) I am thinking about it !!!! and going about my daily chores wearing rubber gloves ! I think we were lucky.

Nick

[tony sayer]

In article , nick smith writes

Quite common heating elements of all sorts. Look upon it as an early warning system that the appliance is about to fail.

No don't remove them, there may come a day when you need that trip protection!. Sort out the other problems first and then the tripping should resolve itself....

[nick smith]

Tony,

That WAS meant to be a joke ! - When we moved in we had a voltage-operated breakerb from ? 50 years ago (overhead feed) which had neither of the earths fitted, either the one to the house wiring or the one to the earth on the plastic water pipe !!

It is still in circuit as a master switch, but now it goes to a new consumer unit with two zones of RCD protected breakers and also a small box of two 6A breakers on non-RCD protected supply for the lights. The fridge and freezer are also on a further separate RCD spur, so any house trips won't take out the fridge/freezer if we are away. Not sure if that is current regs, but seems logical, safer and "it was there when we moved in, Guv" if anyone asks. However, if anyone can comment with constructive suggestions, I would be grateful, not having a copy of the current regs. (not in the trade ! )

Nick

[tony sayer]

In article , nick smith writes

Yes I had noticed later..

How does a voltage operated breaker differ from the current design?.

If it were me I'd protect everything!.

Good idea.

[stefek.zaba]

Massively. To exaggerate, the current (did you mean that as a pun? 'cos it is ;-) one works, the old one doesn't. The voltage-operated design works by making the house 'earth' not a 'true earth', but a conductor to which fault currents flow. When those fault currents make the house 'earth' more than 50V above 'true'/'reference' earth, the voltage-operated breaker trips. So it protects the house 'earthed' metalwork against rising above 50V, making it safe-ish, but does nothing for personal protection in the case of a fault from live to 'true' earth (e.g. out in the garden, copping hold of a live wire while reasonably well earthed, etc.) They were an improvement (in most circs) over nothing, in the case of a no-earth-from-the-supplier feed, but have been superseded by current-balance types in all applications now.

HTH, Stefek

[nick smith]

Hi Tony,

Responses to yours..... severely snipped for ease of viewing..

voice with text !!

As I Understand it, when about 50 volts appears across the earths the unit trips, isolating the house. It only therefore protects earthed appliances and did nothing to protect against shock. I guess it was better than nothing though.

for lights to remain on (active at night) so you don't kill yourself falling down the stairs. The likelyhood of coming into contact with a lighting circuit is deemed small. I suppose a compromise would be to separately protect them with say RCBOs.

Nick