Electric off on two circuits

[Inchy]

Hi all.

A couple of days ago we lost power to all sockets on one circuit (utility, hall and dining room). Trip switch had tripped and when flicked back on would trip again. After a few hours I tried again and this time it didn’t trip. Turned kettle on to test and it tripped again.

So, I unplugged everything from all sockets and now the trip switch stayed on and all seemed good. However, when I plugged anything back into any of the sockets there was no power despite it not tripping.

Then yesterday the wife called to say the cooker and built in microwave - on a separate circuit - had gone off. Checked the fuse board for that circuit and again nothing had tripped but no power to appliances.

So now I have two separate circuits that aren’t tripping but seem to have no power? I’ve tried the obvious of flicking trip switches on and off (including the main one on the board) to no avail. I’m perplexed as to what could cause two separate circuits to fail like this? Electrics were fitted approx 10 years ago.

I’ve got an electrician coming after the weekend but was hoping to try a few simple things ASAP if anyone has any recommendations. Ok with DIY but don’t have any test equipment.

Apologies if my terminology is rubbish.

Any thoughts?

 

[ericmark]

Mice, rats, bats, or other animal which could damage cables? However to day common to have two devices to protect the supply, a MCB often with label like B32 on it, and a RCD often with a label 30 mA or 0.030 amp on it and test button. Both could cause loss of supply. The other thing is if switched on with a fault, or even when tripped some times the leaver can show on but the device is still tripped, physically switch off and on again to ensure not tripped, one can normally feel with the resistance to movement if it is tripping as it is being switched on.

Please state if RCD or MCB which is tripping.

 

[Inchy]

Mice, rats, bats, or other animal which could damage cables? However to day common to have two devices to protect the supply, a MCB often with label like B32 on it, and a RCD often with a label 30 mA or 0.030 amp on it and test button. Both could cause loss of supply. The other thing is if switched on with a fault, or even when tripped some times the leaver can show on but the device is still tripped, physically switch off and on again to ensure not tripped, one can normally feel with the resistance to movement if it is tripping as it is being switched on.

Please state if RCD or MCB which is tripping.

The 1st circuit is on a RCBO B32 (Wylex) and the cooker / microwave ones are marked as NB1-63 B16 (CH(i)NT). They're the only boxes I can see.

 

[JohnW2]

The 1st circuit is on a RCBO B32 (Wylex) and the cooker / microwave ones are marked as NB1-63 B16 (CH(i)NT). They're the only boxes I can see.

As for the first problem, which tripped the RCBO, with some such devices one has to push the lever firmly down (into the 'off' position) before it will reset properly when pushed back up (into the 'on' position). Did you try that?

Do you know where that small CU for cooker/microwave gets its power from? I see that your main CU has an RCBO labelled 'cooker' - what does that do?

Kind Regards, John

 

[Inchy]

As for the first problem, which tripped the RCBO, with some such devices one has to push the lever firmly down (into the 'off' position) before it will reset properly when pushed back up (into the 'on' position). Did you try that?

Do you know where that small CU for cooker/microwave gets its power from? I see that your main CU has an RCBO labelled 'cooker' - what does that do?

Kind Regards, John

Hi John -

There'd been a definite click to the action of pushing the lever on or off, and no obvious resistance, so I think it is resetting properly (we've had numerous power cuts etc in the past and the levers have always worked like this in the past). In terms of the 'cooker' RCBO, this will be a separate one for the electric hob. This is working fine at the moment.

 

[JohnW2]

Hi John - There'd been a definite click to the action of pushing the lever on or off, and no obvious resistance, so I think it is resetting properly...

Fair enough.

In terms of the 'cooker' RCBO, this will be a separate one for the electric hob. This is working fine at the moment.

OK. What about the cooker/microwave CU - do you know where it is fed from? The main mystery, of course, is why two (or more) seemingly totally unrelated things are seemingly misbehaving simultaneously. That CU has three MCBs, labelled 'Near oven", "combi" (I presume the microwave) and "Far oven" - are all three of those appliances now not working? If so, then one can but presume that that CU is not getting electricity from whatever is meant to be feeding it.

Kind Regards, John

 

[Inchy]

Fair enough.
OK. What about the cooker/microwave CU - do you know where it is fed from? The main mystery, of course, is why two (or more) seemingly totally unrelated things are seemingly misbehaving simultaneously. That CU has three MCBs, labelled 'Near oven", "combi" (I presume the microwave) and "Far oven" - are all three of those appliances now not working? If so, then one can but presume that that CU is not getting electricity from whatever is meant to be feeding it.

Kind Regards, John

That's correct, John - there's a main oven, a combi oven / microwave and a steamer oven that those three MCBs cover. All three appliances are devoid of electric.

In terms of where that CU is getting power, I don't know to be honest. Would you expect there to be a connection to the main board or is that not how it's normally set up?

 

[JohnW2]

That's correct, John - there's a main oven, a combi oven / microwave and a steamer oven that those three MCBs cover. All three appliances are devoid of electric.

That's what I thought. Since it is essentially inconceivable that all three circuits, all three MCBs or all three appliances will have become faulty simultaneously, one has to assume that electricity is not getting as far as those MCBs, and maybe not as far as that mini CU.

In terms of where that CU is getting power, I don't know to be honest. Would you expect there to be a connection to the main board or is that not how it's normally set up?

It might possibly come from the main board, but it probably more likely that the supply from your meter splits to feed the main and 'mini' CUs. Could you perhaps provide a photo(s) showing both of the CUs, the meter, incoming supply to your house etc. and what can be seen of cables between them?

Kind Regards, John

 

[Inchy]

That's what I thought. Since it is essentially inconceivable that all three circuits, all three MCBs or all three appliances will have become faulty simultaneously, one has to assume that electricity is not getting as far as those MCBs, and maybe not as far as that mini CU.
It might possibly come from the main board, but it probably more likely that the supply from your meter splits to feed the main and 'mini' CUs. Could you perhaps provide a photo(s) showing both of the CUs, the meter, incoming supply to your house etc. and what can be seen of cables between them?

Kind Regards, John

 

[JohnW2]

Thanks. Where is the ovens/microwave mini CU - in the kitchen? Are the main 'feed" cables going to the main CU and/or that mini one visible and, if so, could we have wider photos which show them as well as the CUs themselves.

What is the labelling of the right-most one of the RCBOs (the B40, next to main switch - which was 'off' when you took the photo)?

Kind Regards, John

 

[Inchy]

Thanks. Where is the ovens/microwave mini CU - in the kitchen? Are the main 'feed" cables going to the main CU and/or that mini one visible and, if so, could we have wider photos which show them as well as the CUs themselves.

What is the labelling of the right-most one of the RCBOs (the B40, next to main switch - which was 'off' when you took the photo)?

Kind Regards, John

(1) oven / microwave mini CU is in the kitchen in a cupboard under one of the ovens. The location is to the right of the outside meter cupboard as you look at the image
(2) no no cables are visible. The main CU is directly behind the outside meter cupboard, so I assume the two cables from the meter that go into our wall are to the main and mini CUs?
(3) the off RCBO is just for an ensuite shower that hasn't been installed. This has always been off.

 

[JohnW2]

(2) no no cables are visible. The main CU is directly behind the outside meter cupboard, so I assume the two cables from the meter that go into our wall are to the main and mini CUs?

That's not "two cables" in the sense you presumably mean - it's just one pair of single-core cables (one Live/Line and the other Neutral). They presumably must 'split' somewhere, into 'two pairs', with one one pair going to each CU, since there seems little evidence that the mini CU is 'fed from' the main one.

Since it would appear that no power is getting to the mini CU, locating where that 'split' happens (and where the cables go) could be crucial. Particularly if the mini-CU is a significant distance from the meter cabinet, it's far from impossible that there is a fuse somewhere in the path, and that could even be your problem.

Kind Regards, John

 

[Inchy]

That's not "two cables" in the sense you presumably mean - it's just one pair of single-core cables (one Live/Line and the other Neutral). They presumably must 'split' somewhere, into 'two pairs', with one one pair going to each CU, since there seems little evidence that the mini CU is 'fed from' the main one.

Since it would appear that no power is getting to the mini CU, locating where that 'split' happens (and where the cables go) could be crucial. Particularly if the mini-CU is a significant distance from the meter cabinet, it's far from impossible that there is a fuse somewhere in the path, and that could even be your problem.

Kind Regards, John

Many thanks for your continued advice, John. The mini CU is only around 6ft from the main CU. If you look at the crude diagram below, the mini CU is the small red box, the main CU the long red rectangle. Black areas are walls and the grey box is the meter box on the outside wall. There are no visible cables at all to either CU - presumably they're behind the plasterboard. The only other visible cable is a thick white one from the mini CU going vertically up, which I assume is the power cable to the oven above.

 

[JohnW2]

Many thanks for your continued advice, John. The mini CU is only around 6ft from the main CU. If you look at the crude diagram below, the mini CU is the small red box, the main CU the long red rectangle. Black areas are walls and the grey box is the meter box on the outside wall. There are no visible cables at all to either CU - presumably they're behind the plasterboard. The only other visible cable is a thick white one from the mini CU going vertically up, which I assume is the power cable to the oven above.

Thanks. Your diagram is clear enough, but it still doesn't answer the question (through no fault of yours!).

As I said, there is only one pair of cables coming from the isolator in the meter cupboard, but those are either splitting (into two pairs) to feed the CUs, or else the mini CU is somehow getting fed from the main one. The former seems the more likely, but it's really a bit naughty if, as seems to be the case, the 'splitting' is occurring somewhere unseen and inaccessible (presumably in some sort of junction box or other electrical accessory). I suppose it's just about possible that the 'thick white cable' you can see is part of the feed from main CU to mini one, but that is fairly unlikely.

I presume that you are certain that there are no other visible 'electrical boxes'/whatever anywhere in the vicinity of either of the CUs or where the cables (presumably) come through the wall from the meter box?

Kind Regards, John

 

[ban-all-sheds]

What type of cable(s) go into the switch of the mini CU?