Why would circuit breaker trip every few hours?

Grenage

Risteard wrote: »

From experience an RCD almost never fails in such a way as it trips for no reason. It is almost certainly an earth fault causing it to trip as they are designed to protect against.

Yeah I've never seen that myself, but the RCD wasn't tripping. In my case the RCD was the cause, and leaving it turned off for a few hours allowed it to function for a while again.

scarletjim

Something else I noticed this morning after it tripped in the night:

When it has tripped, even if I switch all the individual switches off, the main one controlling them (RCD?) still trips. What I mean by that is, when it has tripped, I switch it to the off position, then back to the on position, then push the 'test' button, and it trips back to off. This morning it did this 3 or 4 times, then eventually was ok as a result of me moving the individual switches up and down. Does this suggest a problem with the RCD / Consumer Unit? Or should it do that?

Kiran

If you push the test button when the power is on the RCD will trip out. Its supposed to do that.

scarletjim

Kiran wrote: »

If you push the test button when the power is on the RCD will trip out. Its supposed to do that.

Oh, to ensure the trip is working, obviously yes, sorry that was dumb of me, thanks. So next time it trips, I should ignore the 'test' button, we know that works. I guess I will need to just continue trying different combinations of switches until I understand which one is causing the problem (if any...)

I have spoken to my electrician, who could come later today or tomorrow, but would he be able to do much more than I'm doing, i.e. trial and error? Or would he actually be able to test each individual appliance somehow? (Would take a long time, I expect we have maybe 50 or 60 plugged in over the entire house, such is modern technology...). I'm currently thinking I should continue with my trail and error approach until I at least know which switch is causing the problem, then it will presumably make his job quicker (and so cheaper for me!). Please anyone correct me if I'm wrong, but I don't think it's dangerous for me to leave it another day - it only trips every few hours, so it must be a gradual build up to whatever the problem is, and then it's fine again 10 mins later until it trips again, so presumably the RCD is continuing to do it's job and protect me while the problem exists, yes?

Risteard

A competent Electrician will be able to fault find it. If it is an intermittent fault then it will be more difficult to locate. But it's certainly not a job for you to be messing about with.

scarletjim

Risteard wrote: »

A competent Electrician will be able to fault find it. If it is an intermittent fault then it will be more difficult to locate. But it's certainly not a job for you to be messing about with.

Don't worry, I certainly won't be 'messing about' with anything, I have the utmost respect for electricity. Just thought I'd see what I could learn safely about the problme before asking my electrician to visit - but it looks like I've reached that point so will hand it over to the professional now!

Out of interest though, how will he be able to find it if it only trips every few hours? I'm not intending to put him up for the week at my place! (lol) What will he do, short of inspecting each individual device?

vacheron

scarletjim wrote: »

...... Out of interest though, how will he be able to find it if it only trips every few hours? I'm not intending to put him up for the week at my place! (lol) What will he do, short of inspecting each individual device?

A problem like this is often the result of a permanent fault which is hovering around the threshold of the protective device.

For example, your RCD will trip if the earth leakage current exceeds 30mA. If there is a fluctuating earth leakage current of around 28mA average occurring then this will sometimes nudge over 30mA and trip the device. However the presence of a 28mA earth leakage is unusually high and he will be able to isolate circuits (and then appliances) one by one to find which cable / appliance us causing the high earth leakage.

He should also have with him a multifunction tester which will allow him to perform all the checks required to fully test your electrical system to the requirements of the 17th edition of the wiring regulations.

If it is an RCD fault he will be able to test the RCD independently of the circuit using an RCD tester. He will also be able to check each circuit for earth leakage and insulation resistance breakdown. He will also be able to remove the front panel of your consumer unit and inspect the security and integrity of the wiring to and from each protective device it contains.

Basically he can do quite a lot!

Vacheron (an Electronic Engineer certified to BS 7671 17th Edition and CG 2394 & 2395 Verification and Certification, Periodic Inspection, Testing and Certification of Electrical Installations).

scarletjim

Very informative and helpful - thanks a lot.

Ben84

scarletjim wrote: »

Oh, to ensure the trip is working, obviously yes, sorry that was dumb of me, thanks. So next time it trips, I should ignore the 'test' button, we know that works. I guess I will need to just continue trying different combinations of switches until I understand which one is causing the problem (if any...)

I have spoken to my electrician, who could come later today or tomorrow, but would he be able to do much more than I'm doing, i.e. trial and error? Or would he actually be able to test each individual appliance somehow? (Would take a long time, I expect we have maybe 50 or 60 plugged in over the entire house, such is modern technology...). I'm currently thinking I should continue with my trail and error approach until I at least know which switch is causing the problem, then it will presumably make his job quicker (and so cheaper for me!). Please anyone correct me if I'm wrong, but I don't think it's dangerous for me to leave it another day - it only trips every few hours, so it must be a gradual build up to whatever the problem is, and then it's fine again 10 mins later until it trips again, so presumably the RCD is continuing to do it's job and protect me while the problem exists, yes?

I think some people have responded in a slightly mistaken way because you're saying it trips - but unless the RCD/breakers are turning themselves off, which I think they're not from your descriptions, this isn't the situation. If the switches are not going down it is not tripping, you would instead be losing power, which is a different problem. So to be clear, have any switches ever turned themselves off?

If they haven't, the breakers/RCD may easily have nothing to do with this problem - a weak connection, which seems possible in this situation, can be anywhere in the wiring. It might be a socket in your kitchen, or a junction box under the sitting room floor, for example. Losing power like this without a circuit breaker or RCD turning off won't however be caused by an appliance, so that makes thing simpler.

If it's safe to leave longer is unknown while the problem is unknown. However, if I'm correct and the switches aren't turning themselves off, I think it sounds most like a loose electrical wire somewhere in the household wiring, which would be dangerous to leave. Circuit breakers protect against overloads, and RCDs against things shorting out. They do not however protect against bad electrical connections which are not shorting out. Weak connections heat up. They can get extremely hot and still be drawing far less than the current needed to trip the breaker. The power going out and returning a while later is one symptom of a weak connection as the heating from it will case things to expand, which can break the connection, then it will cool until it makes the connection again, and the cycle repeats. If this is the problem, it isn't limited to only the moments the power cuts out, it's a problem that's going on all the time.

In this situation I would unplug any devices that aren't needed (more current = more heating in poor connections), and get the electrician out soon as possible.

beckstar1975

we had this and then it got more and more frequent ended up me wedged in understairs cupboard 8 months pregnant in pitch black with two wailing children having to call hubbie back from the football.

Turns out rats had chewed through our wiring, obviously the more they chewed the more frequently it tripped until it wouldn't work at all, although meant we could turn that circuit off (sadly downstairs lighting and sockets) and then the others all worked fine until we could get it fixed.

Are rodents a possibility for you?