RCCB Breaker Tripping?

Dave1UK · Oct 3, 2023

Woke up this morning and tried to turn on the computer (work from home) wouldn't power on, checked lights they worked fine. Went downstairs to check the switchboard and only the RCCB breaker was tripped, all other MCBs on. I can narrow this down to it occurring between 06:30 - 07:30 this morning (based on Ring doorbell camera), not that is it of much use knowing this?

As soon as I flipped the RCCB on, it tripped immediately, flipped it on again and it stayed on. An hour later, the RCCB tripped again although this time along with the kitchen MCB. Few minute ago now flipped both on and it's on (currently).

This has never happened before, we haven't bought/plugged in any new appliances, definitely not between 06:30 - 07:30, as all asleep.

In the kitchen we only have 2 fridges plugged in/operating 24/7, microwave (standby) and that is literally it, everything else switched off at mains. I switched off the microwave at mains as well now, so only 2 fridges are plugged into the sockets.

Is there a way to narrow this down further/figure out what could be causing it prior to calling someone in?

Thanks.

Avo Mk8 · Oct 3, 2023

You need to unplug things to isolate the neutral as well as the live, not just turn the switch of a plug off.
If you have an immersion heater, turn it off at its double pole switch local to it. Also unplug kettle, isolate oven etc etc.
Turning MCB's off in the consumer unit doesn't isolate neutral, so best to rely on unplugging things.
It sounds like there's a fault in the kitchen if that MCB tripped?

Hopefully you might find with everything unplugged the RCD will stay reset, and if not you will need an electrician with a tester!

Stating the obvious - things with heating elements and that deal with water are classic items for tripping RCD/ MCB's, eg: kettle, washer dryer, immersion heater, oven etc

Dave1UK · Oct 3, 2023

Avo Mk8 said:
You need to unplug things to isolate the neutral as well as the live, not just turn the switch of a plug off.
If you have an immersion heater, turn it off at its double pole switch local to it. Also unplug kettle, isolate oven etc etc.
Turning MCB's off in the consumer unit doesn't isolate neutral, so best to rely on unplugging things.
It sounds like there's a fault in the kitchen if that MCB tripped?

Hopefully you might find with everything unplugged the RCD will stay reset, and if not you will need an electrician with a tester!

Stating the obvious - things with heating elements and that deal with water are classic items for tripping RCD/ MCB's, eg: kettle, washer dryer, immersion heater, oven etc

Appreciate the swift response and advice.

Will wait to see if it trips again and then actually unplug those appliances in the kitchen. We don't have an immersion heater.

I would assume it is kitchen related, however makes me wonder why the first time it didn't trip, but did second time around?

littlespark · Oct 3, 2023

Is any outside equipment fed from the kitchen area possibly?
Isolate that as well if you can. Water can get into anything even if they say its weatherproof

Dave1UK · Oct 3, 2023

littlespark said:
Is any outside equipment fed from the kitchen area possibly?
Isolate that as well if you can. Water can get into anything even if they say its weatherproof

Nope nothing. Although we do have an outdoor flood light but that's on a different breaker I believe, unless the kitchen breaker tripping second time around with the RCCB was a false positive?

I will take a look at both in either case thanks for the reminder, however no issues as so far yet since the morning.

littlespark · Oct 3, 2023

no issues with the fridges still plugged in? That rules them out for now.
You could try plugging things back in one at a time.... with a couple hours inbetween... and see if it trips again.

Dave1UK · Oct 19, 2023

littlespark said:
no issues with the fridges still plugged in? That rules them out for now.
You could try plugging things back in one at a time.... with a couple hours inbetween... and see if it trips again.

Ever since 3rd October (about 2 weeks ago now) there have been no issues since the initial trip and reset until yesterday again. However this time it wouldn't stay on and kept tripping every 3 minutes or so.

Only way it doesn't trip is with the kitchen MCB off. As soon as you flip it on it trips immediately or within a few minutes. I can almost guarantee it is related to the kitchen area/MCB based on the above? I removed all appliances from plugs in relation to that breaker circuit and it still trips the RCCB with nothing plugged in at all.

I have therefore kept it off for now and using an extension lead from nearby hallway to power the fridge/microwave and kettle etc when needed. Not sure whether this proves the appliances aren't the issue? Would assume so.

Is it possible the kitchen MCB unit is faulty/has developed a fault? I am aware it could be kitchen wiring being wet or whatnot but doesn't seem to make sense to me.

Also to add, the kitchen light flickers for a few seconds when initially being turned on sometimes (has been for months), no other abnormal activity in the kitchen comes to mind. However lights MCB has never tripped but wondering if that may be a sign of something electrical?

davesparks · Oct 19, 2023

Dave1UK said:
Is it possible the kitchen MCB unit is faulty/has developed a fault? I am aware it could be kitchen wiring being wet or whatnot but doesn't seem to make sense to me.

No a faulty MCB can't cause an RCCB to trip.

If it is tripping with all appliances unplugged or otherwise isolated then there is a fault on the circuit.
Faults often don't make sense until they have been investigated.

If you find a decent electrician they will usually be able to find the fault it in a relatively short time frame.

timhoward · Oct 19, 2023

Dave1UK said:
I can almost guarantee it is related to the kitchen area/MCB based on the above?

While it seems more likely in your case, in abstract a large load on one circuit can drive current through a neutral-earth fault (e.g. an outside light full of water) on another circuit, so it isn't a given that the MCB that causes the trip is related to the fault.

It's very frustrating to try and solve this kind of issue without test gear.
A decent electrician would be able to to say which circuit the fault is on within about 5 minutes of entering your home, and prove the problem is resolved. In cases like this with a shared RCD it is usually worth paying for an hour or two of expertise.

pc1966 · Oct 19, 2023

Dave1UK said:
I have therefore kept it off for now and using an extension lead from nearby hallway to power the fridge/microwave and kettle etc when needed. Not sure whether this proves the appliances aren't the issue? Would assume so.

If they don't trip the other circuit when plugged in the are probably OK, but it does not rule out:

A faulty flex that is OK when away from the normal socket.
The other socket is not RCD protected (unlikely, but not to be ignored).
You have too much leakage from everything in the kitchen, etc, combined and so by removing a few items the total is below RCD trip threshold.

Dave1UK said:
Is it possible the kitchen MCB unit is faulty/has developed a fault? I am aware it could be kitchen wiring being wet or whatnot but doesn't seem to make sense to me.

The MCB almost certainly won't be the reason. Wet sockets, junction boxes, or damaged cable(s) are all likely causes.

However, you can get difficult to pin down faults where N-E is shorting (not necessarily on the circuit you find "causes" it) and only above a certain current and on certain circuits does it trip. That is easily checked with an IR test.

Dave1UK said:
Also to add, the kitchen light flickers for a few seconds when initially being turned on sometimes (has been for months), no other abnormal activity in the kitchen comes to mind. However lights MCB has never tripped but wondering if that may be a sign of something electrical?

It is not a good sign, but unlikely to be related. It could be a poor contact (switch, loose cable screw, etc) or it might be a flaky LED driver (assuming not florescent?).

Dave1UK · Nov 22, 2023

So I finally had an electrician come around (someone who was recommended to me).

He started by running few tests on the main switchboard, then sockets and back and forth. Based on his diagnosis it turned out that one socket was faulty/causing an issue (the cable/s anyway - no visible issue on them though i.e. burning or such), however couldn't investigate further as it's under the floorboards so would need access to determine the root issue it seems.

The issue was as I expected in the kitchen. He stated the kitchen wiring is a ring circuit and he basically disconnected the problem socket (no longer works), he also had to disconnect a further 2 sockets making a total of 3 unusable now. We still have a total of 4 functioning sockets.

Within the main switchboard he swapped the B32 MCB to a B20 MCB (spare) as well. He stated this should work fine for the appliances and load for now. He did mention further work will be needed to get it all working again etc.

I am glad he resolved the issue and the kitchen is basically usable again, however not happy that he quoted a different price over the phone and charged extra upon work completion (for no extra work I clearly explained the issue and most likely saved both him/myself some diagnosis time by stating the issue is in the kitchen), I'm sure not everyone is like that however seems to be a big issue within such industries (automotive and such spoils it for others). A shame as he has a lot of 5 star Google reviews and in two minds about giving him 1 star for such a stunt.

Anyhow just here again wondering why the 2 extra sockets had to be 'decommissioned'? Also why swap the MCB from a higher tolerance to lower tolerance?

Included a terrible representation of how the switches are/located, I know the 3 switches are connected like that as the cables hang slightly under the cupboards and can be seen, I also dismantled every single socket prior to calling him over to check if cables are damaged/any moisture. I'm assuming the top one which is high up the wall for the extractor is a spur? Also potentially the cupboard one is also a spur? The red lines with a ? are basically what I would assume/logically would make sense then again I'm not an electrician.

pc1966 · Nov 22, 2023

Dave1UK said:
Anyhow just here again wondering why the 2 extra sockets had to be 'decommissioned'?

Without doing the testing nobody can say, but I suspect he was looking at cables showing an insulation fault and having isolated both ends those happened to be fed from it.

Dave1UK said:
Also why swap the MCB from a higher tolerance to lower tolerance?

In the UK it is common to have a "ring final circuit" (RFC) where all the sockets are wired in a ring, so:

CU -> socket #1 -> #2 ... -> socket #N -> CU

Wired in 2.5mm cable that has a rating of around 20A, but due to the ring and how the current is typically shared you can safely use a 32A supply.

If you break that loop and make two radials, so:

CU -> #1 -> #2 ...
CU -> #N -> #N-1 ...

Then each radial is only safe to 20A so you need to de-rate the supply breaker. If designing for radials, you would put two 20A breakers in, one for each branch.

timhoward · Nov 22, 2023

Well we weren't there, so it's guesswork. My guess is as follows.

He found the 'problem' to be the cable to or from the 'problem socket'.
He then proceeded to change the circuit from a ring final circuit to a radial circuit so the problem cable is no longer in service. He then correctly changed the protective device to comply with protecting the lower current carrying capacity of a radial circuit.
There's nothing wrong with that provided he's looked at the likely loading, especially considering the utility room.

The slightly confusing part is why he then disconnected all the spurs. I can't immediately see a reason but that doesn't mean there isn't one.

This kind of fault finding is hard to quote for in advance; I usually quote two hours to find the issue but not fix it, then when the issue is known discuss the resolution and likely cost with customer.

littlespark · Nov 23, 2023

Yes, you can’t do fault finding on a quoted price… you don’t know what you’re going to come across.

I don’t know why he disconnected spurs either… unless they were spurs from a spur…. Which is wrong on an rfc, but perfectly acceptable on the radial because of the 20A breaker.

Dave1UK · Nov 23, 2023

pc1966 said:
Without doing the testing nobody can say, but I suspect he was looking at cables showing an insulation fault and having isolated both ends those happened to be fed from it.

In the UK it is common to have a "ring final circuit" (RFC) where all the sockets are wired in a ring, so:

CU -> socket #1 -> #2 ... -> socket #N -> CU

Wired in 2.5mm cable that has a rating of around 20A, but due to the ring and how the current is typically shared you can safely use a 32A supply.

If you break that loop and make two radials, so:

CU -> #1 -> #2 ...

CU -> #N -> #N-1 ...

Then each radial is only safe to 20A so you need to de-rate the supply breaker. If designing for radials, you would put two 20A breakers in, one for each branch.

Appreciate the breakdown, the theory seems to make sense. Yeah he just 'decommissioned' and thereafter de-rated, no new parts were added/removed.

timhoward said:
Well we weren't there, so it's guesswork. My guess is as follows.

He found the 'problem' to be the cable to or from the 'problem socket'.
He then proceeded to change the circuit from a ring final circuit to a radial circuit so the problem cable is no longer in service. He then correctly changed the protective device to comply with protecting the lower current carrying capacity of a radial circuit.
There's nothing wrong with that provided he's looked at the likely loading, especially considering the utility room.

The slightly confusing part is why he then disconnected all the spurs. I can't immediately see a reason but that doesn't mean there isn't one.

This kind of fault finding is hard to quote for in advance; I usually quote two hours to find the issue but not fix it, then when the issue is known discuss the resolution and likely cost with customer.

I'm wondering the same regarding the spurs as I just plugged the extractor fan into one of the lower sockets anyway, so unless there is a thing about no. of sockets and MCB limit doesn't seem to make sense. Does make it a little inconvenient to plug the extractor fan on bottom but not unliveable.

In regards to quoting point, maybe but if over the phone you are told there is a RCCB tripping, believe it's a kitchen fault due to kitchen MCB having been off for a week and hasn't tripped the others and can't reset the kitchen MCB as trips immediately (basically a clear job spec - assuming the kitchen is the issue and not a wild goose chase, another story). He asked for a picture of main switchboard and said he will get back prior to scheduling a time to come (assuming some research?). I was fully expecting 2 hours, knew 1 hour wouldn't be enough. Quoted a fixed £75.00 per hour no VAT as wasn't VAT registered (I asked on phone). Spent exactly 1 hour 44 minutes from ringing the doorbell to leaving (don't worry I wasn't timing him but Ring doorbell has timestamps). Didn't have to use any new replacement parts worked with what was there, he identified the issue within the first hour (said he knew what the issue was i.e. that socket and then the next 44 minutes resolved it or so it seems). Ended up with a bill of £190.00, mind you I was going to tip him for the swift resolution but not after that.

I occasionally do some IT repairs on call and we charge a fixed rate per hour as well and can do so and advise the customer of how long it would approximately take based on the problem. We have a lot of elderly clients who unfortunately aren't IT savvy and to be honest not sure why their children don't assist them with most of these issues (ofc with those whereby you can tell they have some). We accept a job based on our expertise and whether we actually can resolve an issue, we go there with our skill set and diagnosis equipment/tools don't charge extra for that separately. Notify them if it may go over the hour, if we spend lets say 1 hour 30 minutes we would offer a discount as well as didn't take the full hour. Bit of a rant but had to get it off my chest!

littlespark said:
Yes, you can’t do fault finding on a quoted price… you don’t know what you’re going to come across.

I don’t know why he disconnected spurs either… unless they were spurs from a spur…. Which is wrong on an rfc, but perfectly acceptable on the radial because of the 20A breaker.

Not sure I follow the 'you can't do fault finding on a quoted price'? If you have a fixed rate per hour, regardless of what the job is, whether you're asked to fault find in 1 room or 10 rooms price should be the same?