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

[davesparks]

If it's two ring circuits then it's possible that someone got confused when connecting up the CU and interconnected two circuits, which would explain two rcbos tripping.

 

[Tom Oxford]

so some match making - Tom are you in Oxford? Midwest - how close are you to Oxford?

Yes, Midwest, are you within reach of Kidlington? I trust my original electrician but it would be good to get another pair of eyes to have a look...

 

[Tom Oxford]

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.

More good stuff: thanks!

 

[Midwest]

Yes, Midwest, are you within reach of Kidlington? I trust my original electrician but it would be good to get another pair of eyes to have a look...

PM me if your original electrician can't assist. Bear in mind if the RCBO's are defective as Richard suggested, their replacements are about £80 each. Hopefully your electrician might just find a simple fault with the wiring.

 

[Tom Oxford]

PM me if your original electrician can't assist. Bear in mind if the RCBO's are defective as Richard suggested, their replacements are about £80 each. Hopefully your electrician might just find a simple fault with the wiring.

Okay, will do, Midwest.

 

[Tom Oxford]

Is the trip random or cab you make it do it?

Sorry for slow reply. As the trip happens much less often than when we use the fan I've seen it as random, but some experimentation just now shows that I can make it happen most times that I switch from speed 1 to speed 2 on the fan, if I do it slowly. I got this idea from reading this other thread:
Cooker hood tripping RCBO - head scratcher - http://www.electriciansforums.co.uk/threads/cooker-hood-tripping-rcbo-head-scratcher.101736/page-2
...which I mostly don't follow (too technical for a layman like myself) but I get the drift that part of the problem was to do with something happening as the fan speed was changed. Our fan speed control is a slider, so switching between speeds means that you can have it momentarily between speeds as you move the slider along.

More information! Helpful or not, is the question?

 

[Octopus]

But you are reporting that a device on circuit A is tripping circuits B and C - which shouldn't happen.

 

[Tom Oxford]

But you are reporting that a device on circuit A is tripping circuits B and C - which shouldn't happen.

Not sure what your point is, sorry...

 

[Richard Burns]

Not sure what your point is, sorry...

The post that you linked to is describing a fault that trips the RCBO to which the circuit is connected. Your fault is tripping an unrelated RCBO so the fault resolution will be different.
Though it is possible that the fault on the socket circuits allows the same effect to occur, just through a fault rather than directly on the circuit, but a bit unlikely.

 

[Tom Oxford]

The post that you linked to is describing a fault that trips the RCBO to which the circuit is connected. Your fault is tripping an unrelated RCBO so the fault resolution will be different.
Though it is possible that the fault on the socket circuits allows the same effect to occur, just through a fault rather than directly on the circuit, but a bit unlikely.

Sure, I just thought any information might be useful. I was answering the question of whether I can repeat the fault at will. Even if the fault resolution is different, I thought the information about the fan speed adjustment might be helpful in working out why the fan causes anything to trip. To my (admittedly layman's) mind, why the fan causes a trip and why those particular circuits get tripped are the two elements of this puzzle.

 

[Octopus]

I think you should give up with internet advice and get your wallet out

 

[Tom Oxford]

I think you should give up with internet advice and get your wallet out

Yes, I think you're probably right.

 

[Octopus]

^^ good man.

The best (and only) thing you can do is keep a log of what trips and when , and what you were doing........ then discuss this with the spark you get to investigate.....but don't be surprised if he "does the basics" to check what's connected to what etc....

 

[CACJL]

It could be by crossed earths in the split load consumer unit.

 

[Octopus]

It could be by crossed earths in the split load consumer unit.

Now that is carp

 

[Pete999]

It could be by crossed earths in the split load consumer unit.

Crossed earths?

 

[weevilward]

Ha ha I bet the sparking hob phenomenon is just coz whoever is looking at the hood is leaning against the knobs on the hob.... I've done that a few times fitting hoods and it scares the sh@t out of you for a second before making you laugh.

 

[Dangerous Brian]

hello, here's a "way out there thought". If the ground and first floor sockets have any surge protection extension leads connected could the operation of the extractor hood cause a voltage transient that is causing the surge protection in the extension leads to dump the transient to earth and so operate the two rcbo's on circuits 5 and 6.

 

[davesparks]

It could be by crossed earths in the split load consumer unit.

Go on then, enlighten us as to what on earth you are talking about, or else I'm afraid I have to call -------- (bovine excrement) on this one.