Circuit keeps tripping, how do we isolate the issue?

springdove

@ThisIsWeird
@BarelySentientAI
@gm0

You have all been so helpful, patient and kind in the way you've explained, I'm very grateful and I wanted to call this out.  Thanks so much and I hope I'm able to pass this on in some way through my contributions to the forum albeit not in the area of electrics!!

Yes, I understand this way more now, and will try this the next time I have a trip.  I hope it's not anytime soon, and I do intend to get an electrician over to have a look at the options. 

In terms of timers, I can only imagine that perhaps some hot water or heating based boiler operation, but I haven't set that to that time at night, so that's odd.  None of the other things you've listed.  

I did notice your point earlier that it might not be the downstairs sockets - I forgot to add a response to that point.  Good shout, it's just that that socket powers our internet and sockets, so it was one of the first I left switched off (as it's the most in use) to see whether that then helps reset the RCD.  Perhaps, as you say, one of the others, which I could do more without, need to be switched off, (maybe the air conditioner which as I say is outdoors!), to see whether this allows the downstairs sockets to be switched on while not tripping the RCD.  

When I was on holiday earlier this year, this fault occurred twice, a few days apart, and at that time, most things were switched off, so our neighbour who kindly reset it for us couldn't really check what the issue was.  Since we returned, I had it once a couple of weeks ago, and then as I say, the last two nights - hence the request for some guidance now here!  A good idea I guess, is to switch off that air conditioner MCB when we next go on holiday. 

No rodents that I'm aware of, but yes we've seen some ants in our back garden, I can't imagine they're a problem!   

In terms of solutions, I'm hoping the electrician is able to identify and resolve the issue - and as it's an 8 year old installation, if there are a few upgrades we can do using those RCBOs, maybe that'll help keep the issue to a minimum.  If you have any recommendations for what I should request be done to help resolve the issue (e.g. telling the electrician I'd like to upgrade/replace the whole unit etc.), please do let me know. 

Thank you once again, I really do appreciate all responses. 

35har1old

ThisIsWeird said:

springdove said:

So, bearing in mind I am indeed a layperson, I think the RCD is protecting all the MCBs to the left of it - but, when I keep one of the MCBs switched off, leaving the others on, and try to reset the RCD, it works, suggesting that the issue is with this particular MCB. 
So, when the trip happens, it's on the RCD in the middle.  If I try to reset the RCD right away, then it wouldn't let me and it keeps tripping back instantaneously.  If I then proceed to switch off the ground floor sockets switch (which is MTN132 B32 - and what I think is an MCB), and then reset the RCD, then the RCD doesn't trip again. 
The following morning, so after a few hours, I am able to safely switch on the ground floor sockets MCB without tripping the RCD. 
I've had this issue as I said, 2-3 times before with days/weeks in between, and now, it's happened on two successive nights.  


In case I hadn't been clear - on all occasions, nothing actively done by us caused the trip, as I see it.  E.g. it wasn't that we switched something on, and at that immediate moment, this tripped.  It just happened day before at 1 am, and yesterday around 12 30 am.  It's happening at night, and so I wonder if it's to do with the temperature or moisture in the air.

Thanks for the good info. And you have a good handle on what's going on.

The two 'big' switches with the blue test buttons are the main switches for each bank of MCBs to their respective lefts, and also provide the RCD protection. You can see they have 0.03A printed on them, and this is the 30mA max of leakage they'll allow before tripping.

Then the two groups of 6 switches are the MCBs as you say, and these do a different task - they limit how much each current each circuit can safely draw before tripping. If one of these babies trip, then that usually tells you that you have a short circuit, or have plugged in too many electric heaters at the same time. That is pretty serious, and usually very obvious.

The fact that turning off the 'downstairs sockets' MCB allows the RCD to be reset might mean it's summat on that circuit, but not necessarily so. As said above, all circuits will 'leak' to some extent, and it's when that adds up to 30mA that the RCD trips. So, it's possible that the 'downstairs sockets' is only leaking, say, 5mA, but all the others are also leaking that amount - so 30mA total! Most likely, of course, some circuits will leak a lot less, and differing amounts.

One way to possibly check is to turn off all the MCBs, and then turn only the 'd-s' one back on. This will likely be a bit of a pain, but if the tripping always happens in the early hours, then it might not matter if the lights aren't available when you go to bed? Just turn them back on in the morn.

So, if you can, try all the MCBs on that left bank off when you go to bed, but only 'd-s' on. If you 'must' have another one on overnight - say one of the lighting circuits - then by all means put that one on too. The idea is to properly trial each MCB circuit on its own if possible.

If you have a night owl in the house, and the tripping always happens at 12-1.30am, then that person could turn them all - except the d-s - off after everyone's gone to bed, and then back on at near 2am before they, too, retire?

Obviously the timing is interesting... Obvious Qs - does a 'time switch' operate anything in your house? Air-con? Cheap-rate overnight electricity? Outside security lights? An electric blanket on a timer? (Don't laugh - mine is... :-(  )

If no tripping with d-s, try each MCB in turn. Then pairs of MCBs!

I had 'nuisance' tripping a couple of years ago. I then tried isolating the lighting circuit of our new extension - bingo! Tripping stopped! Called out the installing sparky, he checked it - nothing. And, of course, the nuisance stopped. He told me another house on our road had similar issues, and he could only put it down to voltage spikes sending the RCD over.

Might be a fridge or freezer 

ThisIsWeird

35har1old said:

ThisIsWeird said:

springdove said:

So, bearing in mind I am indeed a layperson, I think the RCD is protecting all the MCBs to the left of it - but, when I keep one of the MCBs switched off, leaving the others on, and try to reset the RCD, it works, suggesting that the issue is with this particular MCB. 
So, when the trip happens, it's on the RCD in the middle.  If I try to reset the RCD right away, then it wouldn't let me and it keeps tripping back instantaneously.  If I then proceed to switch off the ground floor sockets switch (which is MTN132 B32 - and what I think is an MCB), and then reset the RCD, then the RCD doesn't trip again. 
The following morning, so after a few hours, I am able to safely switch on the ground floor sockets MCB without tripping the RCD. 
I've had this issue as I said, 2-3 times before with days/weeks in between, and now, it's happened on two successive nights.  


In case I hadn't been clear - on all occasions, nothing actively done by us caused the trip, as I see it.  E.g. it wasn't that we switched something on, and at that immediate moment, this tripped.  It just happened day before at 1 am, and yesterday around 12 30 am.  It's happening at night, and so I wonder if it's to do with the temperature or moisture in the air.

Thanks for the good info. And you have a good handle on what's going on.

The two 'big' switches with the blue test buttons are the main switches for each bank of MCBs to their respective lefts, and also provide the RCD protection. You can see they have 0.03A printed on them, and this is the 30mA max of leakage they'll allow before tripping.

Then the two groups of 6 switches are the MCBs as you say, and these do a different task - they limit how much each current each circuit can safely draw before tripping. If one of these babies trip, then that usually tells you that you have a short circuit, or have plugged in too many electric heaters at the same time. That is pretty serious, and usually very obvious.

The fact that turning off the 'downstairs sockets' MCB allows the RCD to be reset might mean it's summat on that circuit, but not necessarily so. As said above, all circuits will 'leak' to some extent, and it's when that adds up to 30mA that the RCD trips. So, it's possible that the 'downstairs sockets' is only leaking, say, 5mA, but all the others are also leaking that amount - so 30mA total! Most likely, of course, some circuits will leak a lot less, and differing amounts.

One way to possibly check is to turn off all the MCBs, and then turn only the 'd-s' one back on. This will likely be a bit of a pain, but if the tripping always happens in the early hours, then it might not matter if the lights aren't available when you go to bed? Just turn them back on in the morn.

So, if you can, try all the MCBs on that left bank off when you go to bed, but only 'd-s' on. If you 'must' have another one on overnight - say one of the lighting circuits - then by all means put that one on too. The idea is to properly trial each MCB circuit on its own if possible.

If you have a night owl in the house, and the tripping always happens at 12-1.30am, then that person could turn them all - except the d-s - off after everyone's gone to bed, and then back on at near 2am before they, too, retire?

Obviously the timing is interesting... Obvious Qs - does a 'time switch' operate anything in your house? Air-con? Cheap-rate overnight electricity? Outside security lights? An electric blanket on a timer? (Don't laugh - mine is... :-(  )

If no tripping with d-s, try each MCB in turn. Then pairs of MCBs!

I had 'nuisance' tripping a couple of years ago. I then tried isolating the lighting circuit of our new extension - bingo! Tripping stopped! Called out the installing sparky, he checked it - nothing. And, of course, the nuisance stopped. He told me another house on our road had similar issues, and he could only put it down to voltage spikes sending the RCD over.

Might be a fridge or freezer 

Damn...damn...

ThisIsWeird

springdove said:

RCBOs are relatively new, I understand, but they are great. 

In essence, they combine an MCB with an RCBO.

So, they detect both a power 'overload' - eg a short-circuit - on each circuit they are fitted too (like an MCB) and the leakage detection of an RCD. Then, only that circuit will 'trip', leaving the others still running. You can then trace the fault in that circuit at your relative leisure - everything else keeps running.

Also it means the RCD won't trip due to a cumulative mA leakage. Each RCBO will only trip if that one reaches 30mA on its own, and that would def point to an 'issue' that def needs fixing.

To upgrade to these RCBOs, you should hopefully be able to retain your existing CU, and 'just' swap the MCBs to RCBOs. They are around £20 each. You could, for example, ask the sparky to replace the 6 MCBs on the left.

Some CU cases will accept the larger RCBOs with little issue, but others may struggle.

Anyhoo, all you can do is ask yer sparky :-)

Grenage

RCBOs are great (although not as awesome as AFDDs).

Your best bet it's just taking the recommendation of a sparky with a decent reputation.

ThisIsWeird

AFDDs - no such thing.

Er, what are they?

BarelySentientAI

ThisIsWeird said:

AFDDs - no such thing.

Er, what are they?

Arc Fault Detection Device - the next big thing after RCBOs.  They claim to detect the disturbance in the electrical waveform to trip when there is the beginnings of a fault, even if that fault isn't drawing significant current (so wouldn't trip an MCB) or involving earth (so wouldn't trip an RCD).

If I remember amendment 2 correctly, BS7671 now requires them for socket outlets in high-risk residential buildings, HMOs, care homes and purpose built student accommodation. (where it used to just recommend the installer considered them) 

I'm still sceptical that they can discriminate between 'normal' noisy AC and 'faulty' noisy AC and think they probably cause nuisance tripping - but I've never tested my theory or come across many of them actually installed.