Tripping RCD in consumer unit

[adds21]

Hi,

We have a problem with our consumer unit RCD tripping, which is becoming increasing irritating.

Basically, it keeps tripping randomly. Sometimes several times in the day, sometimes not for a week or so. I'm pretty sure that, at least some of the time, it's being initiated by a very brief power cut (occasionally I hear our neighbours alarms go off when the RCD trips, and from speaking to neighbours I know we're not the only one this happens to, although I think it happens more frequently to us). I have quite a lot of "stuff" plugged into the ring (including a couple of UPSs, which I know can occasionally cause problems), however there’s no way it’s going to be over 32 amps (hence my feeling that the RCD trips when the power returns, rather than being the cause of the power loss).

We’ve has lots (about 10) of these trips over the last 4 days, which is far more than normal (over the last couple of years we’ve been averaging 1 a week). They can happen any almost any time, including the middle of the night (2am, and 5am this morning), when there is pretty much nothing on except one PC (and quite a lot of stuff on stand-by).

It may sound like the simple answer would be to unplug things from this ring and see if the problem persists, but as it's (usually) so intermittent, I'd rather not do that. I've manually throwing the main power switch to see if it trips, and it does 9 times out of 10 unless I switch off the main ring, in which case it appears fine (at least from memory, I think that was the case, it's been a while since I tried that).

My question is: should a competent electrician be able to locate the problem, regardless of whether it's an appliance, or something to do with the wiring itself? (and if so, can anyone recommend anyone in the BS40 postcode area).

Thanks,

 

[Marvo]

The first thing to do is to rule out all the obvious stuff before looking for more complicated problems. A full test of the supply, the installation and all it's circuits would be the place to start. An experienced electrician would be the thing, hang around, maybe one of our more established members is in your area.

 

[Octopus]

Sounds like a loose connection would be the place to start but no promises it'll be the case. Unless you can keep a list of when the tripping occurs it may be almost impossible to find.... so start by unplugging as much as you can.

 

[adds21]

Sounds like a loose connection would be the place to start but no promises it'll be the case. Unless you can keep a list of when the tripping occurs it may be almost impossible to find.... so start by unplugging as much as you can.

I've got an exact list of the times it's happened over the last year thanks to my server, but I'm a little unsure how this will help? There is no correlation with when certain items are on, and we often get RCD trips in the middle of the night when very little is on, and certainly nothing is being switched on.

This is is my main reason for wondering if an electrician would have the skills/tools/diagnostic equipment required to find the fault (or indeed, if such equipment exists!).

 

[Octopus]

You don't say if you have a single up front RCD or a split board or a dual board. Can you post a picture? The issue is that competent sparks will have equipment, but unless such an issue can be more clearly identified, he may be with you for quite a long time!

 

[dingledong]

you say it also happens to your neighbours ? just the one or more . i have had this before

 

[SJD]

If it is the RCD tripping (and it is a 30mA RCD, not an RCBO), then the assumption is there is too much leakage current. It could be due to (a) the fixed wiring, (b) connected appliances, or (c) a faulty RCD, or some combination of all these.

It is easy to test the RCD with a proper tester, any reputable electrician will be able to do a ramp test that tells you what current it trips at. A 30mA RCD should not trip at all at half the current (15mA), and likely will trip somewhere around mid-20's mA.

It is also easy for an electrician to test the leakage current at the consumer unit with a clamp meter that can measure down to low mA (make sure whoever you call can do this). If this is significant - more than a few mA - then it is time to find out where this leakage is occurring.

Most likely causes are appliances, both intentional e.g. in equipment with mains filters (e.g. a UPS), and unintentional such as fridges, washing machines, oven hob elements, etc that are faulty. Often is it possible to connect/disconnect appliances one by one and watch the leakage current change. There also may be several appliances that on their own don't cause any tripping, but when added together do.

You could also have earth leakage in the fixed wiring, for example damp outdoor connections, but I'd eliminate the connected stuff first, it can be quite time consuming to locate wiring faults, unless you already know there are some likely suspects that should be checked.

 

[adds21]

If it is the RCD tripping (and it is a 30mA RCD, not an RCBO), then the assumption is there is too much leakage current. It could be due to (a) the fixed wiring, (b) connected appliances, or (c) a faulty RCD, or some combination of all these.

Thank you. That's really helpfull infomation. Is it unusal for the circuit to trip ramdomly as ours does? From my (limited) knowledge, I would expect it to trip when under load? Am I correct in guessing that it might be caused by an external surge/brown-out, and it's the act of everything coming back on again once the power is returned which causes the trip?

Thanks.

 

[SJD]

If there is significant leakage, then if the external power drops and then is restored, a temporary surge in the leakage current could well be enough to trip the RCD. In which case, you want to find out what is causing the leakage(s) and remove/reduce it.

 

[Octopus]

You don't say if you have a single up front RCD or a split board or a dual board. Can you post a picture? The issue is that competent sparks will have equipment, but unless such an issue can be more clearly identified, he may be with you for quite a long time!

Would be rather helpful if you responded to this!

 

[adds21]

If there is significant leakage, then if the external power drops and then is restored, a temporary surge in the leakage current could well be enough to trip the RCD. In which case, you want to find out what is causing the leakage(s) and remove/reduce it.

Thanks. That's what I was wondering. I've currently unplugged almost everything from my home office, which is one of the rooms covered by (what I expect is) the suspect ring. I can't conveniently disconnect other stuff from this ring, so this is the best place for me to start. So far, it's been okay for 36 hours, which is a start.

 

[adds21]

Would be rather helpful if you responded to this!

I think it's a split board. It has a RCD switch in the middle, and one side is protected while the other side isn't. Currently, the only circuits on the unprotected side are the ground and 1st foor lighting circuits. All others are on the protected side (two rings, garage, cooker, 2nd floor lighting - I think that's it).

 

[adds21]

you say it also happens to your neighbours ? just the one or more . i have had this before

I'm not sure. I haven't spoken specifically about it to any of the neighbours, so it's only from hearing the odd person complain about it over the last few years that I know some people have issues with their RCD tripping. Might be totally unrelated as far as I know!

 

[Octopus]

I think it's a split board. It has a RCD switch in the middle, and one side is protected while the other side isn't. Currently, the only circuits on the unprotected side are the ground and 1st foor lighting circuits. All others are on the protected side (two rings, garage, cooker, 2nd floor lighting - I think that's it).

The fault could be on any of the circuits protected by the RCD, if its an appliance my money is on the fridge or freezer