Cooker hood trips other circuits on fuse board: what's going on?

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Tom Oxford

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Hi,
I am a newbie to this site, not an electrician but looking or advice. Please excuse any incorrect electrical language: I'll do my best to describe our strange electrical problem.

Sometimes when we are cooking, the fuses for downstairs & upstairs sockets (2 circuits) trip. It's when we use the hob and I'm pretty sure it's the cooker hood (as in the extractor fan) that is causing the problem. The other day a friend turned on the fan and the circuits tripped, without the hob being on. That said, there is a strange phenomenon whereby other kitchen appliances (hood, dishwasher, microwave) when switching on can cause the ignition to spark on the hob, so I feel something odd is going on with the hob too.

The kitchen was installed a year or two after we had the house mostly rewired, and the appliances and sockets in the kitchen have their own circuit. We have had three electricians look at these issues, all doing thorough testing, and none could come up with an answer. The sparking hob is just odd, the fan tripping independent circuits is more disturbing to me. In practice it's just a nuisance (losing internet connection because there's no power to the router, resetting the bedroom clock every time it trips), but I'm always nervous when there's an unexplained electrical issue. Why is an appliance tripping circuits that are totally independent?

Any thoughts, anyone?
 
First off, can you post a picture of the front of your consumer unit showing which fuses/breakers trip and when?

This may help as sometimes it's not a fuse, but another protective device.
 
Is it a circuit breaker that's tripping, or the RCD prior to all your cbs?
 
just consulting the tea leaves. might be a while as i don't drink tea, just beer.
 
SparkyChick said:
First off, can you post a picture of the front of your consumer unit showing which fuses/breakers trip and when?

This may help as sometimes it's not a fuse, but another protective device.
Click to expand...

Here's a picture of what I think of as the main board, which I think is what you mean by consumer unit. Is this what other folks mean by RCD? It's
SparkyChick said:
First off, can you post a picture of the front of your consumer unit showing which fuses/breakers trip and when?

This may help as sometimes it's not a fuse, but another protective device.
Click to expand...

2nd attempt at replying - hope the server doesn't crash this time... Here's a picture of what I think of as the main board, which is what I hope you mean by consumer unit. I did say I wasn't an electrician :) It's fuses 5 & 6 which are tripping, when the extractor fan is turned on (but not every time).

View attachment 36063
 
Murdoch said:
Did any of the sparks clamp the tails to measure the earth leakage?

I'm guessing it's the RCD which is tripping!
Click to expand...

I don't remember being told my tails were being clamped, sorry...

When you say the RCD might be tripping, do you mean there's a fault within the main board? I'm afraid I know very little about electrics so you'll have to explain things in really simple terms...
 
You appear to have RCBOs... these are a combination of MCB (miniature circuit breaker, which protects the cables of the installation against over current - preventing the cables from getting hot and potentially catching fire etc.) and an RCD (Residual current device, which detects current leaking from the circuit, typically through the earth and cuts the power when this leakage is above a predetermined level - for domestic use, this is typically 30mA).

Based on the fact that turning something on on one circuit trips two circuits, you could have a situation referred to as a borrowed neutral, when the neutral wire from one circuit is actually used for another circuit which has it's own live feed. In this case, the current flowing out of one RCBO won't be the same as is coming back into it (it will trip) and the current flowing into another won't be the same as is going out (it will also trip).

I'd also be looking to rule out a neutral-earth fault (where there is an unwanted connection between the neutral wire and the earth wire).

These two issues at least could cause two circuits to trip at the same time.

I'm assuming by the fact that you mention the kitchen has been worked on, the problems started after that? If not, when did they start and had you had anything done immediately before that?

Is this totally repeatable? i.e. does the fault occur every time you turn on the extractor?

You say you've had a number of electricians look at it. Were they all registered with competent persons schemes such as NICEIC, NAPIT? You can check here:- Home - http://www.electricalcompetentperson.co.uk/

I think others will agree when I say, you need to find yourself a decent spark. I'd start by taking a look at the member directory here.
 
you're correct, mid. serves me right for reading posts on phone. deleted my irrelevant post and going to drown myself. ( in beer, you numpty, not the canal ;))
 
telectrix said:
you're correct, mid. serves me right for reading posts on phone. deleted my irrelevant post and going to drown myself. ( in beer, you numpty, not the canal ;))
Click to expand...

I dunno, I keep getting corrected all the time. I put it down to age, poor reading glasses and a lack of quaffable wine or refreshing beer.
 
SparkyChick said:
You appear to have RCBOs... these are a combination of MCB (miniature circuit breaker, which protects the cables of the installation against over current - preventing the cables from getting hot and potentially catching fire etc.) and an RCD (Residual current device, which detects current leaking from the circuit, typically through the earth and cuts the power when this leakage is above a predetermined level - for domestic use, this is typically 30mA).

Based on the fact that turning something on on one circuit trips two circuits, you could have a situation referred to as a borrowed neutral, when the neutral wire from one circuit is actually used for another circuit which has it's own live feed. In this case, the current flowing out of one RCBO won't be the same as is coming back into it (it will trip) and the current flowing into another won't be the same as is going out (it will also trip).

I'd also be looking to rule out a neutral-earth fault (where there is an unwanted connection between the neutral wire and the earth wire).

These two issues at least could cause two circuits to trip at the same time.

I'm assuming by the fact that you mention the kitchen has been worked on, the problems started after that? If not, when did they start and had you had anything done immediately before that?

Is this totally repeatable? i.e. does the fault occur every time you turn on the extractor?

You say you've had a number of electricians look at it. Were they all registered with competent persons schemes such as NICEIC, NAPIT? You can check here:- Home - http://www.electricalcompetentperson.co.uk/

I think others will agree when I say, you need to find yourself a decent spark. I'd start by taking a look at the member directory here.
Click to expand...
Deleted
 
OP from what you've described, your faulty (possibly) cooker hood is tripping circuits 5 or 6, when logic suggests it should be tripping circuit 4, i.e. kitchen sockets? Unless the kitchen fitter, pinched a supply from the upstairs ring to feed the cooker hood?

Think the sparking hob thing is artistic licence, and too much wine when cooking :)

You could unplug your cooker hood temporarily, and see if that stops the fault.
 
Pete999 said:
No I'll continue, just because you are not a member of the CPS doesn't make you a bad Electrician, sorry but that hit a nerve.
Click to expand...

I agree,pete,but the converse is just as true,being registered to anything,does not give any guarantee of competence.

I regularly get asked to follow up on some weird fault,or other,and most likely,the previous investigators,have had splendid,liveried up wheels and togs :)

The OP mentioned that the property had been "mostly re-wired",but the two floors of sockets outlets going off at the same time,may be a concern.
 
The posts that were made earlier in this thread have been lost due to the server move, I replied with this message.

Pete999 said:
No I'll continue, just because you are not a member of the CPS doesn't make you a bad Electrician, sorry but that hit a nerve.
Click to expand...

I know it doesn't Pete and I can see the implication from my comment, sorry for that, but that's not what I meant. I know several great sparks who aren't members of the scams because they don't need to be, but for a householder it's a reasonably good place to start and I feel we should be encouraging householders to check people out using the tools available to them.
 
The OP went on to reply with some details.

When the hood trips the breakers, it trips the two feeding upstairs and downstairs sockets, not the kitchen sockets.

He also went on to state that the kitchen was done about 4 years ago (I think it was 18 months after they moved in which was when the bulk of the rewiring was done) and that all the sparks who'd looked at it were reputable. The fault doesn't occur consistently which would explain why it's proving difficult to track down.

@Midwest suggested disconnecting the hood for a while to see if the fault occurs without it in use.

@Leesparkykent suggested it is a neutral-earth fault on one of the circuits that's tripping.

Beyond that, I can't remember much else :)
 
He did state in one of his replies, that he believed the problem had started when the kitchen was done.

Long time to live with a fault that he believes causes a trip once every one or two weeks.
 
NE fault on hood I reckon. Mine does the same occasionally, CBA to fix/replace. Wife is still waiting for me to clean the windows which I said I'd do February 2016.
 
If I write another reply, will the missing 2nd page of this thread reappear, I wonder...
SparkyChick said:
He did state in one of his replies, that he believed the problem had started when the kitchen was done.

Long time to live with a fault that he believes causes a trip once every one or two weeks.
Click to expand...

Can't believe I took so long to get around to posting on a forum only to choose a day when the server was being worked on and most of my effort was wasted, replies being lost!

I'll try and remember what I said yesterday. Sparkychick got a lot of it but I'll recap.

The extractor is on circuit 4 (kitchen sockets) but it trips circuits 5 & 6 (upstairs & downstairs sockets), usually both at once, though occasionally just one of them. It doesn't happen every time, which would be almost every day, but maybe once every week or two.

When we moved in nearly 6 years ago we had the kitchen ripped out and a lot of rewiring done. It was meant to be just adding/moving sockets and getting the kitchen electrics ready but the existing wiring was apparently dodgy and muddled and so quite a bit of rewiring was done. This was done by a reputable, qualified and experienced electrician. Some 18 months after that we had the kitchen installed, electrics being done by someone else (subcontracted by kitchen fitter). I think this was mostly connecting up.

Yes, it's a long time to live with a fault, but human beings are adaptable ;-) Also, when you've had 3 different qualified electricians test your system and none of them can find the cause, nor seem to think it's dangerous, what else can you do but live with it? Answer that belatedly came to me: ask around on the internet!

Someone seemed to suggest (though I may be taking his comment too literally!) that the issue with the hob sparking when other appliances start up was my imagination but it really does happen, and none of the famous 3 could answer that one either.

In one of my list replies I mooted showing your comments to one of the 3 electricians I've already seen (I know which one seems the most experienced) and seeing what he thought. It's been a couple of years since anyone had a look and I can't remember what they told me they'd looked for, so it may be some of your ideas have been tried already, who knows.

Any thoughts?

Oh, and thanks very much to all of you for contributing!
 
SparkyChick said:
The posts that were made earlier in this thread have been lost due to the server move, I replied with this message.



I know it doesn't Pete and I can see the implication from my comment, sorry for that, but that's not what I meant. I know several great sparks who aren't members of the scams because they don't need to be, but for a householder it's a reasonably good place to start and I feel we should be encouraging householders to check people out using the tools available to them.
Click to expand...

For what it's worth, as a layman, I felt Sparkychick was just making a suggestion of a good place to start in finding a good electrician and not casting any aspersions...
 
Last edited:
Murdoch said:
I'll try again.

Op has it worked properly since the kitchen works?
Click to expand...

The extractor has tripped those other two circuits for as long as I can remember but I can't swear whether it started as soon as we had the kitchen fitted or not, sorry. I can't think of any work that's been done or anything that's happened since the fitting that may have triggered the phenomenon. Ditto the hob sparking thing.
 
Don't know if anyone else has asked, and my head hurts when I try to read back through the posts, but these 3 Electricians that have looked at your problem, did they leave any reportsafter they hAD
 
A appliance on circuit 4 tripping circuits 5 and 6 sounds implausible
You have a cooker hood outlet that trips the up and down sockets,because it is located in the kitchen may not mean it is part of the kitchen ring

If it was wired into both the up and down ring (bridging both)it may be possible to operate a very low current appliance much of the time and perhaps cause tripping of one or both the Up and/or the Down Rcbos on occasion only,the imbalance of the trip may be within its threshold with just a fan

The hob igniter operating when it feels like doing so is very strange and other than guessing its some sort of capacitive charge across a faulty item then I would be at a loss to even consider this is real
 
Murdoch said:
So that's a no then!

Can you post a picky of your fuse board?
Click to expand...

I did this already but it looks like the server move may have lost it so here it is again.

IMG_4050.JPG
 
Des 56 said:
A appliance on circuit 4 tripping circuits 5 and 6 sounds implausible
You have a cooker hood outlet that trips the up and down sockets,because it is located in the kitchen may not mean it is part of the kitchen ring

If it was wired into both the up and down ring (bridging both)it may be possible to operate a very low current appliance much of the time and perhaps cause tripping of one or both the Up and/or the Down Rcbos on occasion only,the imbalance of the trip may be within its threshold with just a fan

The hob igniter operating when it feels like doing so is very strange and other than guessing its some sort of capacitive charge across a faulty item then I would be at a loss to even consider this is real
Click to expand...

If I manually flick off the fuse for circuit 4 the extractor fan stops; not so with circuits 5 & 6.

When you say you would be at a loss to even consider this is real (hob sparking), do you mean you don't believe it happens? Cos it does! :)
 
Midwest said:
OP from what you've described, your faulty (possibly) cooker hood is tripping circuits 5 or 6, when logic suggests it should be tripping circuit 4, i.e. kitchen sockets? Unless the kitchen fitter, pinched a supply from the upstairs ring to feed the cooker hood?

Think the sparking hob thing is artistic licence, and too much wine when cooking :)

You could unplug your cooker hood temporarily, and see if that stops the fault.
Click to expand...

Why don't you first try disconnecting the cooker hood by turning off at the wall switch you mention. This should be a double pole switch, which should electrically disconnect it from it's supply. If the fault not longer manifest itself, then you could start looking at having the appliance tested for faults.

This does not explain why the hood on circuit 4, is tripping circuits 5 & 6. Sometimes with the best or worse intentions, kitchen fitters deputise themselves as electricians, and can make a right hash of things, this of course is not true of all kitchen fitter electricians. If, as it already has been suggested, these circuits have been cross connected, may be one possible line of inspection.

I note that your fuse board is populated with MEM ALB321 mcb's. I don't believe you could purchase an MEM ALB321 RCBO (Residual Current Breaker with Overcurrent)? You can however, I'm told, convert them to an RCBO, using a field fit RCD Pod. MEM are no more, but spares are obtainable from EATON, well not spares but replacements. Clutching at straws, perhaps these kits have not be assembled as per manufacturers instructions?

You seem to have some confidence & trust in the electrician who originally rewired your property. Why don't you see if he/she will come back and investigate these faults?

It is difficult to carry out fault finding from afar. The label on your fuse board suggest you are due an inspection anyway. :)
 
Midwest said:
Why don't you first try disconnecting the cooker hood by turning off at the wall switch you mention. This should be a double pole switch, which should electrically disconnect it from it's supply. If the fault not longer manifest itself, then you could start looking at having the appliance tested for faults.

This does not explain why the hood on circuit 4, is tripping circuits 5 & 6. Sometimes with the best or worse intentions, kitchen fitters deputise themselves as electricians, and can make a right hash of things, this of course is not true of all kitchen fitter electricians. If, as it already has been suggested, these circuits have been cross connected, may be one possible line of inspection.

I note that your fuse board is populated with MEM ALB321 mcb's. I don't believe you could purchase an MEM ALB321 RCBO (Residual Current Breaker with Overcurrent)? You can however, I'm told, convert them to an RCBO, using a field fit RCD Pod. MEM are no more, but spares are obtainable from EATON, well not spares but replacements. Clutching at straws, perhaps these kits have not be assembled as per manufacturers instructions?

You seem to have some confidence & trust in the electrician who originally rewired your property. Why don't you see if he/she will come back and investigate these faults?

It is difficult to carry out fault finding from afar. The label on your fuse board suggest you are due an inspection anyway. :)
Click to expand...

Thanks, Midwest: all sound advice. I think I will get our original sparky back and run everyone's suggestions past him. I'm pretty sure he tested to make sure that the three circuits in question were properly independent of each other bu there might be something he hasn't thought of. You're quite right about an inspection being due too: I only noticed that when I posted the photo! Slightly embarrassing...
 
You won't diagnose and fix this on a forum. You need a competent local spark with time, a mft and a clamp. Meter......

And money to pay them

P.s. I'm sure those are rcbo's
 
Murdoch said:
You won't diagnose and fix this on a forum. You need a competent local spark with time, a mft and a clamp. Meter......

And money to pay them
Click to expand...
Fair comment. It's just that after having had 3 competent* local sparks draw blanks I thought I'd try a different tack for some input. Which I've got :)
* Though I guess some might measure competency by the ability to sort out the problem...!
 
Because each circuit you have is individually protected by an RCBO an earth fault on one circuit cannot affect another circuit.
However it is slightly possible, especially as the board is quite old, that the RCD portion of perhaps both circuits 5 and 6 is becoming damaged and perhaps sensitive to voltage transients, which could be generated by the cooker hood and possibly by the ignitor.
I would more probably expect that the problem is more related to a fault on one or both of the socket circuits or weak RCDs.
A potential sense check might be to get an electrician to initially test if the RCBOs function correctly and secondly to swap the RCBOs between circuits and see if the fault follows the RCBO or not.
Obviously if the tripping remains with the RCBO then the RCBO should be changed, however it would have to be a secondhand one as they are no longer available.
If the fault does not follow the RCBO but remains with the circuit then the concentration should be on testing the circuits for, probably, neutral earth faults either internally to the circuit or between circuits 5 and 6.
 
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