Oven occasionally trips both rcd and mcb

[stuartR1963]

HI, I have an ignis akl906wh 2.6Kw oven and Occasionally it trips the both the rcd and 32 amp mcb (which plunges the entire flat into darkness) as well as blowing the 13 amp fcu located behind the oven (which is a pita as it means i have to pull out the oven to replace the fuse. The issue is nothing is ever obvious whenever this happens no flashes/bangs and none of the heating elements in the ovenhave blown, fan motor hasn't seized everything in the oven continues to work.
What could be causing this intermittent issue? Behind the oven is an outlet plate which supplies the hob and next to this is an fcu which supplies the oven in question both the fcu and outlet plate are controlled by the 45amp cooker control switch above the worktop.
Should this fcu behind the oven even exist? I'm used to just seeing an outlet plate and never seen this setup before.
Sounds stupid but is it possible the 13 amp fuse in the fcu is getting tired overtime as its running near its limit and when it eventually blows it creates enough current to trip the mcb/rcd or is more than likely the oven is faulty? But if its the latter what could it be because nothing is obvious.
Thanks

 

[stuartR1963]

Bump, I have no idea how old the oven is but it was here when I moved in (5 years ago) the flat is rented and the landlord has sent an electrician round to inspect the oven but he couldn't work out what was wrong it? The oven is currently working but no doubt it will trip the power again some time in the future.
What could it be because its getting pretty annoying having to pull out the oven to replace the 13 amp fuse?
Thanks

 

[JohnD]

Oven tripping RCD is usually a cracked or eroded heating element. Any electrician or appliance repairman should know that and it is an easy and inexpensive fix.

As you are getting a blown fuse and tripped MCB as well, it might possibly be that the element is really, really bad and is shorting

Or that there is an additional fault, such as a cable damaged by having the oven stood on it, or a water leak.

Do these faults occur when the oven is turned off?

FCU concealed behind the oven is shoddy design and installation.

 

[stuartR1963]

Oven tripping RCD is usually a cracked or eroded heating element. Any electrician or appliance repairman should know that and it is an easy and inexpensive fix.

As you are getting a blown fuse and tripped MCB as well, it might possibly be that the element is really, really bad and is shorting

Or that there is an additional fault, such as a cable damaged by having the oven stood on it, or a water leak.

Do these faults occur when the oven is turned off?

FCU concealed behind the oven is shoddy design and installation.

Hi, the oven never trips anything when it is turned off, it just trips the power randomly (both rcd and mcb as well as blowing the fuse behind the oven) this can happen sometimes months apart to sometimes just a few days apart it's just random really.
I'll check the flex and inspect the heating elements and report back I may well have accidentally damaged the flex when pushing the oven back.
I did think an fcu behind the oven seemed daft as I've never seen this before and have always just seen an outlet plate supplying both the oven and hob.
Thanks

 

[EFLImpudence]

Just to clarify:

Do you mean that when it happens, all three devices trip or is it sometimes one, sometimes another?

 

[stuartR1963]

Just to clarify:

Do you mean that when it happens, all three devices trip or is it sometimes one, sometimes another?

Hi, all of them fuse, mcb and rcd all operate whenever this happens which plunges the entire flat into darkness.
Thanks

 

[stuartR1963]

Hi, I suspect the answer is no but is it worth getting the fcu replaced for another outlet plate and upgrading the flex to the oven to 2.5mm if it isn't already? At least then I would'nt have to keep pulling out the oven to replace the fuse whenever it decides to trip the power again. The mcb for the cooker is 32 amp so I'd imagine it would protect a 2.5mm flex in the event of a short circuit? The oven is rated to 2.6kw so I don't believe the oven could overload the flex unless the fan motor stalls?
Thanks

 

[EFLImpudence]

Hi, I suspect the answer is no but is it worth getting the fcu replaced for another outlet plate and upgrading the flex to the oven to 2.5mm if it isn't already? At least then I would'nt have to keep pulling out the oven whenever it decides to trip the power. The mcb for the cooker is 32 amp so I'd imagine it would protect a 2.5mm flex in the event of a short circuit? The is rated to 2.6kw

Yes, that would be acceptable.

 

[stuartR1963]

Yes, that would be acceptable.

Thanks I will see about getting that done, am I correct in thinking this oven could never overload the 2.5mm flex unless somehow the fan motor were to stall/seize? I'd imagine the 32 amp would protect the 2.5mm flex in the event of a short circuit?
Thanks

 

[EFLImpudence]

As above, there must be a Line to Earth fault somewhere.

As it does not happen instantly when the oven is turned on, it would appear to be something moving when heated - element presumably.
Random faults are very difficult to find.

Thanks I will see about getting that done, am I correct in thinking this oven could never overload the 2.5mm flex unless somehow the fan motor were to stall/seize? I'd imagine the 32 amp would protect the 2.5mm flex in the event of a short circuit?

Yes, that is the accepted thinking and would be the situation if your hob and oven were a cooker.

A small fan is unlikely to cause a problem.

 

[cjcoffin]

Thanks I will see about getting that done, am I correct in thinking this oven could never overload the 2.5mm flex unless somehow the fan motor were to stall/seize? I'd imagine the 32 amp would protect the 2.5mm flex in the event of a short circuit?
Thanks

Assuming it is a dedicated circuit for the hob and cooker protected by the 32A mcb then they should both have outlet plates, and the cables should be 4 sq mm. 2.5 is insufficient as it will be protected against short circuit but not overload even though this is unlikely.

Sorry I have no idea about the intermittent fault, have experienced leaky elements in the past with both a brand new cooker and a very old one. Elements that are in regular use don't usually suffer from leaky insulation.

Fan motor stalling might burn out the winding but probably not trip the breaker. Presumably you can see/hear if it is working?

 

[EFLImpudence]

Assuming it is a dedicated circuit for the hob and cooker protected by the 32A mcb then they should both have outlet plates,

Outlet plates are not the only acceptable method.

and the cables should be 4 sq mm. 2.5 is insufficient as it will be protected against short circuit but not overload even though this is unlikely.

"433.3 Omission of devices for protection against overload

433.3.1 General
A device for protection against overload need not be provided:
...
(ii) for a conductor which, because of the characteristics of the load or the supply, is not likely to carry overload
current, provided that the conductor is protected against fault current in accordance with the requirements
of Section 434
..."


2.5mm² will be fine.

 

[cjcoffin]

Outlet plates are not the only acceptable method.

Maybe but you haven't suggested one. A fused connection unit concealed behind the appliance itself is not to my mind an acceptable method and the OP himself suggested an outlet plate which would at least avoid the need to keep changing the fuse and the temptation to put a nail in it.

Am also considering that a future occupant might on seeing the 32A circuit rating replace the oven with something drawing more than 3kW e.g. a complete cooker for which I would regard 4 sq mm as the min usual size cable.

Kitchens are a bit like the wild west but I have always tried to keep to sensible arrangements like fcus above the appliances they control and not inside cupboards etc but OTOH not cooker control units directly over the cooker.

 

[EFLImpudence]

Maybe but you haven't suggested one.

No, but you implied that outlet plates was the only way to do it.

A fused connection unit concealed behind the appliance itself is not to my mind an acceptable method

I agree. The fuse is not necessary.

and the OP himself suggested an outlet plate which would at least avoid the need to keep changing the fuse and the temptation to put a nail in it.

I know and I told him that would be acceptable.

He could, of course, have moved the FCU to an accessible place, fitted a plug and socket, plugged into the kitchen ring circuit, connected it to the hob, etc.

Am also considering that a future occupant might on seeing the 32A circuit rating replace the oven with something drawing more than 3kW e.g. a complete cooker for which I would regard 4 sq mm as the min usual size cable.

Then that will be up to them and nothing to do with Stuart.

Kitchens are a bit like the wild west but I have always tried to keep to sensible arrangements like fcus above the appliances they control and not inside cupboards etc but OTOH not cooker control units directly over the cooker.

Ok. Others might disagree.

 

[stuartR1963]

As above, there must be a Line to Earth fault somewhere.

As it does not happen instantly when the oven is turned on, it would appear to be something moving when heated - element presumably.
Random faults are very difficult to find.


Yes, that is the accepted thinking and would be the situation if your hob and oven were a cooker.

A small fan is unlikely to cause a problem.

Hi there just thought I'd give you an update, I found out what was causing the oven to trip the power intermittently, removing the metal cover behind the oven there was a scorch mark on the metal cover and a charred uninsulated spade connector which connects to the fan heating element. I ordered a replacement insulated connector and its now back up and running. I can only conclude what you told me that as the oven heats up either the element or the metal backplate is moving slightly due to the heat which has caused a short circuit buy hopefully now the new insulated connector should prevent this happening in the future if there is any movement.
As for the fcu behind the oven I've decided to leave it in place as I've figured if the elements blow or anything goes wrong with the oven is going to have to be dragged out anyway.
How the previous electrician missed this is just beyond me I can only conclude he didn't remove the metal cover?
Anyway just thought I'd give you this update and let you know all is now well.
Cheers