RCD (sometimes) trips on switching OFF an ELO

[topquark]

Your theory would be correct if the RCD is inclined to trip at a level below it's 30mA rating and nothing else in the house has a low-level leakage but this oven does. That would explain the "new" problem. I don't have the kit for insulation resistance testing or testing the RCD but would modestly claim the "skill". I am a pro mechanical engineer and that requires a good working knowledge of industrial electrical installations but do not claim to be an "electrician" beyond the commonsense DIY stuff.
I now think it is unlikely to be the wiring in the light of another helpful post which pointed out that if that were it the trips would not occur only on the On/Off function.

Can I surmise that you have a clamp meter and have tested the trip current present on the cooker circuit?

 

[sparkinlee]

...in the light of another helpful post which pointed out that if that were it the trips would not occur only on the On/Off function.

As he who posted what I think you're referring to, I'd point to the use of the word 'probably' in that post!

 

[charlhu]

OK - if there is not a faulty component to replace then a total frustration and waste of time to contact the moronic world of Merloni.
I did think of taking the cooker circuit off the RCD. As far as I understand the regulations, it is not compulsory for it to be on RCD - only ground floor sockets that may be used for appliances outside and water hazard locations such as near showers .... Yes?
No, not an ideal "solution", but I am confident there is no wiring problem with the oven which makes it dangerous to use otherwise it just would not operate at all and I have been using it without problem for several months now with only this occaisonal RCD trip when switching off after use. The "now you see it now you don't" nature of the problem is typically a control one (the business side of the oven either works or it doesn't) and will probably defy identification. As you will know the "expertise" of manufacturer's technicians is limited to replacing an expensive motherboard. More sense to be gleaned from a forum like this as has already been the case in a couple of hours.

 

[telectrix]

one thought has just occured to me. it may be that the swich on the unit is double pole and one pole is breaking a fraction of a second before the other on switch off, thus causing a momentary inballance,

 

[telectrix]

sorry missed out and/or arcing.

 

[charlhu]

Apologies for the misquote!
Nevertheless, in the light of the helpful comments of "topquark" I think that you are "probably" right! Given the history of storage, something a bit sticky in the control motherboard seems the most plausible explanation. My chances of getting that sorted with Merloni are the proverbial snowball's. So, if you read my last reply to "topquark", then if it does not infringe the regulations, I may just have to take the cooker circuit off the RCD. There is a difference between "desirable" and "essential" and an element of commonsense needed.

 

[charlhu]

Unfortunately not but I am not averse to buying any kit that helps me fix this myself.

 

[charlhu]

Thanks for your comment but wouldn't that be most unusual for a domestic appliance?
Also, as mentioned, I also get trips by leaving the oven "on" and switching off with the cooker switch so that rules out a physical problem with the oven switch.

 

[charlhu]

Further to my earlier reply - replying to the post of "telectrix" made me remember something that "possibly" ( to use the "mot du jour") works against the control problem theory. The trip can also occur if I turn the oven programme selector switch back to the first "on" position which only turns on the oven lights (next click would be "off") and then switch off the cooker switch. Seems to me that takes the oven out of the equation?

 

[topquark]

Further to my earlier reply - replying to the post of "telectrix" made me remember something that "possibly" ( to use the "mot du jour") works against the control problem theory. The trip can also occur if I turn the oven programme selector switch back to the first "on" position which only turns on the oven lights (next click would be "off") and then switch off the cooker switch. Seems to me that takes the oven out of the equation?

Probably takes the oven heating elements out of the equation, but not the internal wiring, the light itself, or even possibly the control circuit.

 

[charlhu]

I like that. Could be just the lighting circuit. I will take the bulbs out and see what happens.

 

[Des 56]

I think at the minimum you should carry out an insulation resistance test on the appliance and the circuit before considering using an unprotected way for that circuit

The Rcd may have for quite some period been at the threhold of operating without doing so due possibly to other appliance leakage on the same Rcd
Have you tried the cooker without other loads protected by that Rcd unplugged

Possibly now that a different cooker, with possibly greater earth leakage has been connected,the thresold has been breached, noticed only when that particular function is operated on the cooker,inductive loads in the cooker like the fan may play a part

As stated the rcd operation should also be verified as sound

 

[pushrod]

Could be more than one problem - cumulative earth leakage acting on the rcd, dodgy rcd, isolator arcing when being switched under load, faults in cooker too . Too many variables to be honest unless you can rule some out through testing.

Charlhu when you reply to a particular person use the "reply with quote" it makes it easier to see what post you are talking about, and so easier to follow. If you've been helped by someone use the "thanks" or "like". Good luck think you might need it to sort this with out testing - your thompson local/ yellow pages might show a cheap appliance repair guy who you can question as to what test equipment he has.

 

[topquark]

I like that. Could be just the lighting circuit. I will take the bulbs out and see what happens.

You won't be able to see to burn the food then

Bon chance, a de suite!

 

[nickblake]

So you have a hob and oven connected in a junction box , mmm that always rings alarm bells to me especially if its a modern oven that can be plugged into a socket why i hear you ask ,well if and i say if the oven is the type i have mentioned then it is supplied with its own cable and normally is 1.5mm , connected to a cooker circuit protected by a 32 amp MCB ,doing this would provide no overload protection to the oven cable , this wiring should be protected by a FCU easily done behind the cooker circuit or should be on its own circuit mean while back to the problem , it could be the start of the RCD becomming fault and you may find that it will start to trip occasionally when other items are switched on or off, this should be checked , claire is right in some ways , its could well be a switch problem where the switch is sticking closed when its switched off before opening thus not making a clean break of the connection causing an imbalance /slight arch always a possability , if its an RCD fault then the only real way to find out would be to replace the RCD , a Ramp test will show the tripping current how ever testing may not show up the described fault