Intermittent RCD problem - what to do?

[GrahamGKD]

Hi Folks,
Help needed from the electrical experts on here please – again!!
Our house RCD has started tripping very occasionally (like 5 weeks ago and then again the other evening). Both times it has happened the RCD will not reset initially but the fault goes away within a minute or so so there is no time to try and work out where in the the fault is coming from. Our consumer unit is way before 17th Edition so the whole shooting match goes off (including the freezer).
My workshop is now on a completely separate circuit from the meter so it is nothing to do with that (thanks Brightspark – that was a great solution for the workshop problems I was having a while ago). The only external wiring we have is a set of outside lights but they are on a double pole switch and that circuit was switched off at the time. It was raining the second time this happened but we think it was dry the first time. There is some wiring down the cavity and under the floor so I guess there is potential for something to be getting damp.
So – what can I do – thoughts I’ve had so far include:
Wait for the problem to become more frequent – the freezer is the most critical thing and I could buy a cheap one and stick it in my workshop temporarily.
Change the RCD – I had some problems with it tripping with my compressor starting and plasma running before I split the workshop supply off – could the RCD be flakey (it’s a GE, maybe 18 years old).
Fit a new 17th Edition CU - at least then the source of the problem would be divided down the middle and the RCD would be replaced with two new ones. Only problem might be that some of the tails coming into the CU may be on the short side.
Any suggestions would be much appreciated – Thanks.

 

[madkayaker]

RCD'S do fail but the only way to find out is to preform a ramp test to see what current it trips at. there could be a leakage fault in the house wiring causing the fault or it could be an appliance doing it. if it trips during the night and when no one is there then the top candidates are fridges and freezers doing it when the pumps start running . my advice would be to get a decent repeatable spark in to do an "installation condition report" the the new name for the periodic if you use the new name when asking you will fast tell if the spark is aware of the new changes to the 17th edition

 

[awemawson]

My house RCD kept tripping - usually at night, and trying to isolate a circuit that was causing the problem proved impossible. Not suprising as when in desperation I changed the RCD it hasn't happened since. So moral of the story is, YES rcds do fail.

 

[brightspark]

a simple insulation [megger ]test on the instalation is the first thing to identify any earth leakage . if any is found unplug all apliances and turn off all isolator switches eg cooker emersion heater . central heating then re test . if alls clear test each appliance till the fault is located . if the fault is on the fixed wiring remove all fuses or turn all the breakers off and disconect all the neautral cables of the bar . re test each circuit till faulty cable is found and leave disconected . re conect all good circuits and trackdown the faulty part of the circuit by disconecting at joints or behind sockets till found . its not rocket science but u would need an insulation tester minimum. better still if u have an rcd tester to test the tripping current in case of a faulty trip a clamp on milliameter is also handy to measure any leakage in short get a decent electrician to do a test as u probably wont have the equipment to check

 

[GrahamGKD]

Thank you all for that advice – I don’t have an insulation tester, only a Fluke 115 multimeter – I understand it needs to be tested for leakage at a fair voltage (500v?) which the multimeter won’t do? There do seem to be a few insulation testers on ebay for not too much money but I wonder if they are rubbish?
I know an electrician locally so I’ll see how much he would charge for the ‘installation condition report’. I guess I’m most worried that if the problem is a motor starting or water dripping onto some wiring somewhere that these tests won’t show it up though?
There is a second had GE RCD on ebay for £15 including post so I could swap that out and see if the problem goes away?
So far the problem has only shown itself when we have been at home using stuff – the washing machine is top of my suspect list at the moment.
Thanks Again,

 

[madkayaker]

any item of equipment with a heater or motor in is very high on the list earth leakage is normal for equipent but a rcd will trip between 0.5 and 1x its rated current so 15mA to 30mA. my veiw is if the wireing is maybe 18years old it will not hurt to get the whole thing looked at to find out what other problems might be lurking unknown of rather than just solving the RCD one. With a bit of thorght its possible to fit a new RCD within a seperate enclosure next to the consumer unit. I wouldn'tbe looking at getting second hand RCD'S of eBay.

 

[GrahamGKD]

Thanks Madkayaker – yes, you mention heating elements – for a while I thought it might be the water heater in the washing machine as that doesn’t get activated very often (we normally run the water hot so that the machine takes hot water from the tank) – unfortunately I have ruled that out now.
I agree – it is time we had some testing done on our system.
Once again, thanks for your advice.

 

[madkayaker]

if you need any help understanding the results the testing gives feel free to get in touch

 

[silverstag]

Ask your local electrician if he has a portable appliance tester. You just plug your items, kettle, washer etc. into the tester one at a time and the tester carries out a series of tests on each item. Any problems will show up in the test results.

 

[Wedg1e]

I used to have a similar problem, luckily I realised it always seemed to occur after I'd been rummaging for stuff in the loft.
A good search unearthed ('scuse the pun ) a length of twin and earth cable that had been crushed against a joist edge by a careless boot and was leaking between conductors when disturbed.
New length of T&E sorted it (plus a re-route)...

 

[GrahamGKD]

Thanks silverstag - yes - I guess he will have a PAT tester - I'll see what he suggests when I get hold of him.

Thanks Wedg1e - good point but I don't think my problem is like that - I've made sure my cabling is pretty much out of the way or protected.

Thanks for your generous offer madkayaker - the guy I have in mind is in NZ at the moment, back tomorrow, I think (which probably means he has already left NZ!). He has been away for a few weeks so it might take him a day or two to get around to my problem! No further occurrences yet.

Cheers,

 

[Ducati]

Hi Graham.

This is a bit of an odd one but similar to yours.

Is your washing machine slightly noisy ?

A neighbour had a similar intermittent fault that was eventually traced to the washing machine.

The fault only occurred when washing her husbands work clothes, boiler suits, on a long wash and when on a rinse / spin cycle, but not on every work clothes wash, no problem though when doing the rest of the washes.

What had happened was that the seal for the drum bearings had started to leak.

When on the spin / rinse cycle and a fine mist of water was getting on the PCB etc and causing the trip.

The bearings were slightly worn and possibly the weight of the boiler suits allowed the shaft to move allowing more water through the seal which got on the drum pulley and belt.

New drum bearings and seals all was well again.

 

[GrahamGKD]

Hi Graham.

This is a bit of an odd one but similar to yours.

Is your washing machine slightly noisy ?

A neighbour had a similar intermittent fault that was eventually traced to the washing machine.

The fault only occurred when washing her husbands work clothes, boiler suits, on a long wash and when on a rinse / spin cycle, but not on every work clothes wash, no problem though when doing the rest of the washes.

What had happened was that the seal for the drum bearings had started to leak.

When on the spin / rinse cycle and a fine mist of water was getting on the PCB etc and causing the trip.

The bearings were slightly worn and possibly the weight of the boiler suits allowed the shaft to move allowing more water through the seal which got on the drum pulley and belt.

New drum bearings and seals all was well again.

Brings a smile to my face that one, Ducati.

Last time it tripped the missus had overloaded the machine - when she said she thought that might be the problem I told her not to be silly as the problem was an earth leakage one rather than the load issue you might associate with overloading the machine!

The washing machine is top of my list and has been for a little while - when I get a minute I'll pull it out and get the back off to look for anything obvious.

Cheers,

 

[awemawson]

Rubbish machine design that lets a failing seal spray onto ekectrics. Designer 'should' realise that seals fail and electrics should be positioned where drips cannot get at them

 

[ford34/2]

m/c check

easy quick check, front loader- open the door and see what movement you have by lifting the drum up, any movement suggests bearings, failing probably because the seal went in the first place.

Stan

 

[Wedg1e]

easy quick check, front loader- open the door and see what movement you have by lifting the drum up, any movement suggests bearings, failing probably because the seal went in the first place.

Stan

I have an Ariston (I know, I know - it was cheap ) that managed about 2 years before making the dreaded grumbling of a failed bearing.
Stripped it down and sure enough the main bearing had more play than a Sunderland schoolie after three lager and blacks.
Off I went to local bearing supplier: no problem on the bearings but the guy pointed out that the shaft seal would be a funny size (it was) - a cunning scam that washing machine makers use to ensure you can't just fit a standard oil seal
So I dropped in to the local washing machine cowboy's place who told me they couldn't supply just the seal as Ariston haven't made it available: you have to buy the whole spider, shaft, bearing and seal complete - £180 to you guvnor - I only paid £225 for the bl88dy washer!
Anyway, I decided to proceed with the rebuild using the original seal as it looked in reasonable condiition... smeared a bit of silicon grease on it on reassembly and thought it might last a few washes until I could stump up for a new machine.
That was four years ago, it's still going strong...

The original bearing was an open-frame type so the slightest weep of water was able to get in. Planned failure? I should say so.

 

[GrahamGKD]

Our washing machine is a Bosch and it has functioned faultlessly for quite a few years now.

I did the check suggested by Stan (checking for play in the bearing) - there is no sign of play or any roughness in the bearing when the drum is rotated. Also no undue noise when the machine is running. That doesn’t mean it isn’t the machine causing the problem though!

I'm waiting to see what is running the next time it trips and also for the sparky to come back to me on the testing suggested by madkayaker.

 

[Ed.]

Also had a RCD that was continually tripping, up to 8 times a night, for about 4 weeks, calling in a Sparky who couldn't find anything wrong, called the power company, same thing, couldn't find anything wrong, by this time I was a walking vegetable with the lack of sleep, I have about 4 UPS's in the house running the network, TV entertainment setup and a couple of aquariums, so when the power goes off, they all have alarms which activate, so I said stuff it, and went out and got a replacement RCD for $35, No more problems. Apparently the first one got way to sensitive with age.

 

[brightspark]

rcd

Also had a RCD that was continually tripping, up to 8 times a night, for about 4 weeks, calling in a Sparky who couldn't find anything wrong, called the power company, same thing, couldn't find anything wrong, by this time I was a walking vegetable with the lack of sleep, I have about 4 UPS's in the house running the network, TV entertainment setup and a couple of aquariums, so when the power goes off, they all have alarms which activate, so I said stuff it, and went out and got a replacement RCD for $35, No more problems. Apparently the first one got way to sensitive with age.

itsnot rocket science. any good electrician should be able to pinpoint problem within half an hour having the correct gear to test. 1st an insulation tester[megger ] and then an rccd tester allso a clamp on milliameter for testing leakage under load. ive done hundreds of callouts for housing asociations and some well known home insurance companys advertised in all that time all were sorted 1st time within the hour . only a couple of re visits just for multiple or intermittent faults guess work isnt an option

 

[madkayaker]

any DECENT sparky should be able to find a tripping fault but as many don't understand how a RCD works many just look and scratch head or start trying to bodge it so it wont trip!