Main RCD Tripping

[Groover75]

Old house with a 1960s fuse box and RCD. Since we bought the place the main RCD (but not the circuit breakers) randomly trips. Getting tired of it and no idea how to proceed.

Typically it trips once every few months. It did it today. It last did it three weeks ago, twice in a row separated by five minutes. Before that it was at least six months since the last trip.

When it happens it can be the middle of the day or the middle of the night. Raining or not raining.

Usually pressing and holding the RCD reset button doesn't reset it the first time but immediately trying again clears the problem.

I called an electrician last year and he said it would be very difficult to isolate but might be related to the pond electrics. I put a separate RCD on the pond electrics, similar to this one:

http://www.diy.com/departments/bq-black-1-gang-240-v-13a-240v-rcd-adaptor/189965_BQ.prd

I was hoping that if it was the pond electrics then only that RCD would trip, but that's not the case. I don't know if the pond RCD is failing to trip, as after each main RCD trip I just hammered on the test/reset buttons for the pond RCD.

I cannot identify any pattern to this.

Not sure if it is related but I will mention it anyway: since moving in 1.5 years ago there are certain lamps and fixtures that continually blow bulbs. Bulbs last only a couple of months. All other lamps/fixtures don't chew through bulbs.

Thanks.

 

[JohnW2]

I called an electrician last year and he said it would be very difficult to isolate but might be related to the pond electrics. I put a separate RCD on the pond electrics, similar to this one:
http://www.diy.com/departments/bq-black-1-gang-240-v-13a-240v-rcd-adaptor/189965_BQ.prd
I was hoping that if it was the pond electrics then only that RCD would trip, but that's not the case. I don't know if the pond RCD is failing to trip, as after each main RCD trip I just hammered on the test/reset buttons for the pond RCD.

When you have two RCDs in the same circuit, there's no guarantee as to which one (or both) will trip in the case of a fault, so your experiences do not prove very much.

Since you're talking about a plug-in RCD adaptor, the implication is that the pond electrics 'plug in' to a socket. If that's the case, can't you just unplug the pond stuff for a while and see if the main RCD still trips - or is there a reason why you can't leave the pond without electricity for a while?

Kind Regards, John

 

[Groover75]

Since you're talking about a plug-in RCD adaptor, the implication is that the pond electrics 'plug in' to a socket. If that's the case, can't you just unplug the pond stuff for a while and see if the main RCD still trips - or is there a reason why you can't leave the pond without electricity for a while?

Kind Regards, John

Thanks for the reply John. Electrics = waterfall = oxygen for fish. If I leave it unplugged for five months it doesn't prove anything because I've gone six months between RCD trips before.

So far the pond RCD has never tripped on it's own. Yes, stupid previous owner brought it into a socket.

What I was hoping to avoid was spending time and money replacing X, Y, Z in the hope that it would fix the problem but without being sure. For example I have a home office with several PCs, surge protector, etc. which I have read could cause issues.

Note that the electrician didn't test anything, just made a guess...

 

[ban-all-sheds]

I called an electrician last year and he said it would be very difficult to isolate

Sadly he could very well be right.

//search.diynot.com/forum_sear...tbytime=0&author=&search=Search+Forum&stype=0

Did he do any tests, either of the circuits or the RCD?

but might be related to the pond electrics.

It might.

Fridge/freezer is another possible culprit, given your description of the pattern of trips.

I was hoping that if it was the pond electrics then only that RCD would trip, but that's not the case.

No - with RCDs in series there's never any guarantee which will trip first, or that only one will trip.

Do you only have 1 RCD? Do you have a section of the CU not on it? If so, any spare spaces in it?

Do you have a lot of electronic devices (PCs/printers/TVs/DVDs/etc)?

 

[JohnW2]

Thanks for the reply John. Electrics = waterfall = oxygen for fish. If I leave it unplugged for five months it doesn't prove anything because I've gone six months between RCD trips before.

Fair enough. The truth, of course, is that if trips can be that infrequent, it could be next-to-impossible to discover the cause - whenever you do, or change, anything, you might have to wait at least 6 months to discover whether it had made any difference.

What I was hoping to avoid was spending time and money replacing X, Y, Z in the hope that it would fix the problem but without being sure. For example I have a home office with several PCs, surge protector, etc. which I have read could cause issues.

Yes, that is one of the many possibilities. However, as above, with such infrequent trips, it would be very difficult to identify/eliminate the cause.

Note that the electrician didn't test anything, just made a guess...

If there is something 'marginal' going on which occasionally gets 'pushed over the line', and then causes a trip, then some tests might be useful. However, if (as is quite possible), the problem causing the trips is itself very intermittent, tests undertaken at any point in time might well reveal nothing wrong.

Sorry that I can't be more helpful, or encouraging! Other people may have some other ideas.

Kind Regards, John

 

[plugwash]

If tests don't reveal anything and you want the problem solved then IMO the only real option is to divide the installation up among multiple RCDS.

If the problem is lots of little leakages adding together and sometimes pushing over the line then this dividing up may well fix the problem. If the problem is an intermittent issue then it will at least give you a better idea of where the problem is and reduce the inconviniance caused by the trip.

 

[ban-all-sheds]

For example I have a home office with several PCs, surge protector, etc. which I have read could cause issues.

I was too slow with my question.

They can indeed cause issues - collectively they could lift the "background" leakage current to almost the trip threshold of a single RCD. And with months between trips you'll never be able to identify any appliance (if there even is a single miscreant one) by leaving it off.

Note that the electrician didn't test anything, just made a guess...

You can get guesses here for free, so I hope you didn't pay him too much.

There is the possibility that your RCD is particularly sensitive - shame he didn't rule that out.


You might find that the only cure is to split your socket circuit(s) up as much as possible, at least get the office on its own one, and to put them on their own RCDs.

 

[ban-all-sheds]

[TOO]

Not my day today

[/SLOW]

 

[JohnW2]

Did he do any tests, either of the circuits or the RCD?

Note that the electrician didn't test anything, just made a guess...

No - with RCDs in series there's never any guarantee which will trip first, or that only one will trip.

When you have two RCDs in the same circuit, there's no guarantee as to which one (or both) will trip in the case of a fault, so your experiences do not prove very much.

Do you only have 1 RCD? Do you have a section of the CU not on it? If so, any spare spaces in it?

Old house with a 1960s fuse box and RCD

Do you have a lot of electronic devices (PCs/printers/TVs/DVDs/etc)?

For example I have a home office with several PCs, surge protector, etc. which I have read could cause issues.

Kind Regards, John

 

[Groover75]

Thanks for the replies.

There is one empty space on the panel but it's so old it's not possible to get anything for it's particular form factor anymore apparently...

I was hoping there was some clever way of combining lots of patience with spending a modest amount to get a smoking gun when it happened again.

Looks like we will plan for a new panel at some point in the future as suggested.

Thanks.

 

[plugwash]

When you get a new consumer unit make sure you specify one with seperate RCBOS (combinations of MCB and RCD) rather than RCDs covering large groups of circuits.

 

[JohnW2]

Looks like we will plan for a new panel at some point in the future as suggested.

Indeed. The best, albeit not the cheapest, solution would be to get an 'all-RCBO' CU, so that each circuit effectively had its own RCD - you would then know what circuit had caused a trip, and it would only kill that one circuit. Also, as has been suggesting, with RCBOs, splitting the sockets circuits up a bit (e.g. office, pond, the rest) would make the task even easier.

Edit: too slow again!!

Kind Regards, John

 

[ban-all-sheds]

A whole bunch of stuff which shows that he simply did not think of the possibility that I might have started my reply before anything else had been posted.

 

[JohnW2]

A whole bunch of stuff which shows that he simply did not think of the possibility that I might have started my reply before anything else had been posted.

Possibly, if it took you a long time to compose your reply - everything I quoted was posted at least 20 mins before you posted your reply, most of it appreciably earlier than that.

Kind Regards, John

 

[333rocky333]

So far the pond RCD has never tripped on it's own. .

By that do you mean it has tripped together with the main RCD or has the pond rcd never tripped.

If it has its possible there is either a fault on the pond as you suspected
OR
you have a cheap plug in RCD on the pond that turns off with loss of power, caused by the main one tripping.

If the pond is suspect get, a LATCHING RCD that does not trip on power loss.
hopefully then, but not quarenteed, if it then trips, either on its own or together with the main RCD, it will point to the suspect pond.

I once had a problem on a rcbo circuit, tripping randomly, we temporary used 3 plug in RCDs at a time, till we eventually found the one appliance causing it