3 phase RCCB tripped, won't reset

[naylorpd]

Hi, in my garage I have a 3 phase RCCB that has tripped and I just can't get it to reset, even with all the downstream MCBs switched off. Bit of a nuisance really as mother in law has no power to her flat above the garage and the garage door and front gate don't work.

I tried uploading photo but "The uploaded file was not an image as expected." so had to make do with PDF...sorry.

I've tried switching off every MCB that is downstream of the RCCB but even if I can get the RCCB to reset for a minute or so as soon as I switch anything on (just MCBs, not load) it trips again. And once or twice I can reset the RCCB for a minute or so, with no other MCBs on, and it will trip again.

Clearly there is a damp problem in the wall, but actually we are well past winter and ambient temperatures are rising - already around 18-20C. Everything inside the CU looks dry. Cables in the wall are in plastic pipe (UK T&E), except the incoming 3 phase which is SWA, and I guess the 3P link to the upstairs flat is also SWA - can't remember...

Just not sure where to look or what to check. Normally I would turn on the MCBs one at a time until I found which one was causing the trip - but this time it seems to be any of them, or none of them. Actually I've never really had electrical problems here.

I'm in Azerbaijan, I don't have access to a qualified electrician. Apart from design and first fix I did most of the installation myself, about 5 years ago.

Thanks

 

[Julie.]

Irrespective of what voltage measurement is made from time to time, or the fact it seems to be ok at the moment, I would suggest that there is a neutral to earth fault somewhere in your system.

It may be in the fixed wiring, it may be in some appliance which is plugged in sometimes, or anywhere.

Stray current will flow via this route, even with your line connections open, if this goes above ~30mA then the rccb will trip - with no actual load.

If I was checking for this, I would disconnect or open the incoming supply such that all 4 lines are open - then check the resistance n-e. I would be looking for several Meg ohm. And would use a 250/500v insulation resistance test rather than a multimeter - although a multimeter may indeed find the fault.

If it is ok, then I would be checking the appliances for a n-e fault as given the 3v it may not be a permanent short.

 

[Mike Johnson]

I take it that when trying to re-set the RCCB you unplugged everything including the oven, fridge and freezer in your house and the flat.

 

[pc1966]

See if you can borrow an insulation tester, if not I see them listed on eBay for $US 50 or so (no idea how good / reliable, but maybe worth having if you do any eletrical DIY of note).

 

[Mike Johnson]

I take it that when trying to re-set the RCCB you unplugged everything including the oven, fridge and freezer in your house and the flat.

Forgot to add, your MCB's are single pole so just switching them off still allows the neutral to be connected to any appliance plugged in, therefore a fault on one of the appliance's could be the problem, once you have done this try to reset the RCCB, if it still will not set then disconnect all of the neutrals from your board and try again, if that works, then reconnect each neutral in turn.............you know the rest.

 

[naylorpd]

OK, so this is now sorted, nothing wrong with the wiring, though I guess I still have my 3V N-E to contemplate.

One place I hadn't thought to look was an outhouse which has a combi boiler and water pump. The water pump had a ridiculously short power cable so I plugged it into an extension lead and stuffed that behind the pump (several years ago). Out of sight, out of mind. Not sure if the pump was dripping or some rain had got in when the door was left open, but the extension lead was distinctly wet when I found it yesterday (with an experienced electrician who came armed with RI tester and earth leakage meter).

So I've rewired the pump with a long enough cable to reach the power socket - at which point I found that although the old cable was three-core, the earth wire wasn't connected. Also now fixed.

 

[pc1966]

Good to hear you found a clear problem and it is now fixed!

Don't worry about the N-E voltage if it is less than tens of volts, a couple of volts is perfectly normal.

 

[Mike Johnson]

pc1966 that seems to send the wrong message i.e. that a N-E fault is nothing to worry about?

 

[pc1966]

pc1966 that seems to send the wrong message i.e. that a N-E fault is nothing to worry about?

No, an N-E fault is a serious business, but if you are seeing 3V between N & E it is a good indication there is not such a fault!

Basically my point is the neutral voltage will not be exactly zero in real life, and if it is below tens of volts then it is within the sort of range that is probably OK. If you see more than the order of 5-10 or so volts it would be worrying as that contributing possibly above its share of the 5% drop in supply that might be considered normal-ish.

 

[Lucien Nunes]

Qualified by the fact that this particular installation is known to be TT, so it's reasonable to expect N & E to be at different voltages. Wherease on a TN-C-S system, significant voltage between N & E at the origin, or between PEN and something extraneous, would merit investigation.

 

[marconi]

naylorpd: May I ask why and what took you to Azerbaijan? Just curious. No insult will be taken by me if it is none of my business to know.

 

[naylorpd]

@marconi no problem...
Back in 1997 my accounting career was in a bit of a rut, my employer was slowly going down the tubes and I had started job-hunting, not very successfully. I went on hols and came back to look in the Financial Times for the Thursday when I was away, that's when all the financial jobs appear. There was one for BP in Azerbaijan - after I'd figured out where that was I applied, really just for the interview experience with no expectation. I was interviewed by my prospective boss and we really hit it off. Three months later I was here.

My first thought was to do about 3 years, make a bit of money and come back to the UK to start afresh. But in the first month I met my wife-to-be, who was a young opera singer. It took a bit of time to get going but eventually we married and started home-building here. Twenty three years later, here I am still.

 

[pc1966]

That is a great success story!