Anomalous Tripping by RCD

[ronaldtkw]

Our Crabtree 80A RCCB has worked well since 2000, but last night its MAIN switch tripped, without any of the individual circuits tripping. This was when only a few lights a TV and computer was on in the house. It would resist switching on again, usually tripping again in minutes. But if we switched off ALL the individual circuits, switched on the main switch and then just a select 1 or 2 circuits, it would usually hold. Over the next few hours, we could go on to adding the other circuits again.....until the main switch trips again.

Have tried selectively switching the individual circuits on or off, but have found no pattern. Electricians so far seem to have little idea. Can anyone help?

 

[pompeygit]

If the RCD is not faulty, and it does sound ok then you are leaking current to earth somewhere. Have you done any DIY lately (screws or nails into floors walls ceilings)?. It could be you have 1 appliance leaking a fair current to earth and a kettle or washing machine is tipping it over the balance. Did the electricians do an Insulation Resistance test ? Have you tried disconnecting all appliances and switching on all circuits? If OK start plugging in appliances 1 at a time and see if this causes RCD to trip.

 

[leeco]

i had a simler problem with my rcd it turned out to be the dishwasher motor

 

[ronaldtkw]

Back again. The electricians have been in and out. They first identified the fault as the pond pump in the garden, which I promptly disconnected. That evening, the MAINS switch cut! Next electrician identified a control unit on the central heating system. Plug out. 3 hours later the switch trips.
I pulled the plug on any appliance which may involve moisture....kettle, coffeemaker, washer, fishtanks, fridge, etc....then plugged these in at 5-10 minute intervals. No trip. 30 minutes later it trips.
I can go to bed with just the ring mains and water heater circuits on( which keeps the fridge and aquariums going, and it'll still trip in the middle of the night.
After tripping, I can reset by first switching off all the circuits, then switching on the MAIN, waiting a few minutes, then switching on 1 or 2 circuits. This will hold for 2-3 hrs, even if I add further circuits. If I do this first thing in the morning, after it's tripped overnight, it'll hold for some 6 hrs before tripping again. Any ideas? The electrician is due again soon....

 

[AMEdinburgh]

Our experience with this random tripping was a combination of small earth leakages from various items and a big earth leak (but not enough on its own) from the fridge, hence the randomness of the tripping. You might find it necessary to PAT test (I know the T is test but everyone calls it that) all your plug in stuff and see what's good dubious and bad. A new fridge sorted the problem (now 4 years)

A couple of electricians who looked at the problem before this had all sorts of theories that weren't right and the RCD was returned and tested by the manufacturer as one of them certified the fault laid there.

A time consuming and frustrating experience

(DIYer not spark)

 

[ronaldtkw]

Hi Everyone

Thanks for the feed back. It does seem to be some complex effect, from more than one source. Strange how it seems to build up. If the main switch is reset in the morning after having tripped at night it can hold for 5-6 hours. When it then trips, switching all circuits off and resetting before switching some of them on again will give 2-3 hours.

The electrician came in with a replacement RCD and wired it in. That was at 15.30h. It's now 18.08h and still holding.....

Luckily this is all being done under household insurance( Homeserve) for the electricity. But not sure what happens if the new box doesn't cure it. As you suggest, we may have to test each and every appliance....

 

[JohnD]

Is every circuit in the entire house controled by a single RCD? this is bad practice, especially if you have a pond or aquarium which would be much better on its own.

Cooker circuits are not usually on an RCD, do you have one?

Can you provide a photo of the consumer unit?

I have a favourite way of dealing with RCD problems, but it would cost you extra. Ask your electrican what he would charge to fit RCBOs (you would have to pay for this as it would be an Improvement not a Repair)

p.s. you do know about mice gnawing cables?

 

[ronaldtkw]

Yes, John, everything went through that RCD. That's the way the electrician did it when we moved into the house, and we didn't know any better. But mice? With 2 cats, we've never had a problem.

To update: the new RCD tripped at 1930h, 4 hours after it was fitted. Despair. So it was back to downing all the circuits, resetting the MAIN, and switching on the MCBs one at a time. Next morning, Saturday, we found it had tripped again in the night, so we reset again at approx 8 am. I switched on the immersion heater in the airing cupboard for hot water and had a quick shower before we all went to London for the Motor Show. I had intended to switch it off afterwards, but forgot in the rush. On return home at after 1900h we were surprised ithe RCD had NOT tripped. My elder daughter had looked in about lunchtime to check and if necessary reset, but it was holding. This Sunday morning, right now. it continues to hold.

What does that say? The hot water tank was piping hot yesterday, after being on all day. I had previously switched it on for say 20 minute intervals, which had not prevented the tripping. Come to think of it, when the central heating used to be on, the tripping had not occurred, even with loads of damp washing in that airing cupboard.[/img]

 

[JohnD]

yes, immersion heaters (being a watery appliance with a heating element) often get earth leakage as they age.

Note that turning off the MCB may not prevent tripping, since an RCD will trip from a Neutral-Earth fault as well as from a line-Earth fault. However the On/Off switch on the wall will (should) be a DP switch if reasonably modern. All other appliances need to be unplugged, not just switched off, since many switches are single-pole.

Can you post a pic of your Consumer Unit? And also the incoming power cable, company fuse, meter and the wires between them (especially any thick green-and-yellow ones) //www.diynot.com/forums/viewtopic.php?t=129539

Do you live in a rural area or have an overhead supply? Do you have an Earth Spike into the ground? this might be why the house was oriiginally wired with one RCD for the whole house (though you are seeing now the drawbacks of this arrangement). there are better ways of doing it.

 

[ronaldtkw]

I did upload an image in the album named RonPics, but have been unable to transfer it into the forum messages here.

The house is a semi built about 1976, and smack in the middle of Marshalswick in St Albans....hardly very rural now, but at the time it was on the edge of fields.

I'm no electrician and don't know what the earthing arrangement is for the house. Has the heated-up water tank dried out a source of earthing in the airing cupboard? It's been off now since last night, and I'm waiting to see if the tripping comes back eventually. But this seems a lucky clue for the struggling electricians to isolate the problem. Before, they were getting nowhere with their little hand-held meters.

 

[JohnD]

I did upload an image in the album named RonPics, but have been unable to transfer it into the forum messages here.

Untitled

• ronaldtkw
• 1 Aug 2008
• 1