RCD (sometimes) trips on switching OFF an ELO

[charlhu]

I recently replaced an old electric cooker with an up-market multi-function ELO and ceramic hob that I had kept in storage for 4 years - a simple swap at the cooker switch. The Wylex domestic CU was put in 4 years ago and incorporates a WRS 80/2 30mA RCD and has never given any problem. There is never a problem switching the ELO "ON" and operating it but every now and then (but not always) when the programme selector switch is turned back to the "OFF" position the RCD trips. This can also happen if the cooker switch is turned off. The ELO and hob go through the same cooker switch via a junction box but the hob never causes an RCD trip. I don't want to have expensive call-ins on a problem that cannot be reproduced at will especially when it is unclear whether it is an electrical or an appliance problem. As I see it, if there was a leakage problem with the ELO it would always trip the RCD when switched on. I wonder if it might be a cable fault? I used the existing cables still connected to the two units to feed the junction box. Have rechecked the connections half-a-dozen times.
Grateful for any advice/suggestions!

 

[claire_r]

Neutral isn't switching as quick as live when you turn it off, imbalance, rcd trips

 

[sparkinlee]

Neutral isn't switching as quick as live when you turn it off, imbalance, rcd trips

I was thinking of something like that, but it still must indicate a fault condition somewhere. Ie there must still be a leakage to earth to allow the unbalanced current to flow.

My guess would be an issue with the appliance, but it could be with some of the new cables / junction box I think the OP said had been added.

And (responding to something in the first post) no, a fault with the appliance would not necessarily appear all the time because it may be related to a particular function or action, such as turning off.

Get someone in with a test meter, who can also check that the cables which were up to supplying the old electric cooker are up to powering a ceramic hob and ELO (Electric Light Orchestra??!)

 

[Had8Lives]

I was thinking along the same lines Claire_r . Could be a sticky relay or thermostat. You did say it has been in storage.

 

[charlhu]

Many thanks - but if that is the problem - what is the solution?

 

[charlhu]

I did think perhaps there is now something "sticky" in the controls due to storage but it only happens with a simple on/off operation - even if the oven has been left to cool down first (even overnight) so that rules out a relay or thermostat?

 

[sparkinlee]

The solution would be to get an electrician in who can fully test the circuit RCD itself, and also PAT test the appliance to see if the speculations above are correct...

After that, repair whatever turns out to be faulty!

 

[charlhu]

Thanks for your contribution. ELO = Eye Level Oven (Sorry!).
Cable from board to cooker switch is the built in wiring. I put this on to the junction box and from there fed the two units using the cables that were used in their previous location and still connected up. I wondered whether there might now be a partial internal insulation breakdown in the one cable that is causing it?

 

[sparkinlee]

I wondered whether there might now be a partial internal insulation breakdown in the one cable that is causing it?

Yes, it might be that, although if it was that the tripping would probably be more random and not seeming to be related to a particular action.

My main point is... it could be any of these things, so best to get it tested rather than keep speculating!!

 

[topquark]

Not sure I understand what's meant by neutral not switching as quickly as live, the neutral won't normally be switched, only the live?

There is a potentially dangerous appliance that should be checked out. What's unusual in this case is the tripping happening when the oven is turned off.

Obviously if there is an imbalance the current is going somewhere, that's either to earth (via cpc) or to a device capable of charge storage (most likely a capacitor) or via a sufficiently inductive load.

Assuming the circuit supplying the appliance checks out OK. I'd then start by contacting the manufacturers technical dept and see if there are any compontents in the ELO controls that might explain the behaviour. Then IR testing the oven (once it has been warmed up, don't forget to isolate it after warming though ).

 

[charlhu]

Thanks but, as stated in my post, that is the costly solution that I am trying to avoid to what may be a simple problem. Logically,the RCD is fine since, as also said in my post, there was no problem before I installed the oven in question. If I can first identify whether the problem is wiring or the appliance then in the first case I can fix it myself and in the second case probably need to call in an appliance technician but at least that is only one call-in.

 

[topquark]

Not sure how you can assert that the RCD is fine. Just because it didn't trip before. The RCD will trip at a certain current, nominally 30ma of leakage (or imbalance between line/neutral) ..... some will trip as low at the low 20ma's and still deemed to be working correctly.

Do you have the necessary equipment (and skills) to do an insulation resistance test on the wiring?

 

[charlhu]

You are right that, being a domestic installation, it is switched on the live only. Unfortunately, this is a "Scholtes" top-range unit that I bought and used in France and the brand (now owned by the Merloni Group) is no longer distributed in the UK. Any consumer who has had experience with the technical support for any of their products (e.g. Indesit) would probably recommend the hemlock option!
I would have more confidence in a competent independant repairer who can tackle any brand but finding one is also a problem. Any dicky component is likely to be a "bought -in" item and findable. BTW, I am in London E18.

 

[topquark]

I wasn't suggesting that the componet would be faulty ... it may be a valid part of the control design, but may explain the occasional nuisance tripping.

If there is no socket on the cooker isolator switch then you could consider taking the circuit from a non rcd protected side of the CU, but I wouldn't recommend it.

Another option to consider would be a more fault tolerant RCBO (type C) for the cooker circuit. These are nomally used for circuits supply motors and other largely inductive loads. However! You need to prove the cooker is OK for use before going down that route.

 

[charlhu]

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.

 

[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

 

[telectrix]

there's always the alternative




SALAD

 

[topquark]

there's always the alternative
SALAD

That one of your cryptic mneumonics for a sequence of tests Tel?

 

[pushrod]

there's always the alternative




SALAD

or ours would be TAKEAWAY

 

[Des 56]

there's always the alternative

SALAD

An excellent suggestion but it has its flaws

The Salad solution may only be a partial solution

Who is to say the meat eaters in the family will accept this
A deep roast in a suitable oven exceeds the taste of cold chicken portions I'm sure

 

[charlhu]

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

I think you may have hit it!
When I originally bought and installed this oven in France it had a cable with a continental plug and there was socket in the kitchen for it on a separate circuit from the hob. I put it down to differing electrical systems (e.g. they use fused circuits, individual neutrals back to the board, etc) so without further thought I just put it on to the cooker circuit as I described. Seems that could be the root of the problem. Also your theory of "cumulative small leakages" reaching the trip threshold makes a lot of sense and I will try to check it out by disconnecting everything in sight though ithat may not be conclusive as it doesn't trip "on request".
Either way it seems that it would be best to have a separate circuit installed. I don't entirely understand your wiring proposal - If it is cabled back to a 32A MCB on the board it somehow has leakage protection separately from the existing RCD? If I go that route I'll get an electrician in to do it but would like it to be a case of him implementing a viable solution not confronting a problem.

 

[charlhu]

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

Bon chance, a de suite!

Just temporarily as a diagnostic. Anyway, I am a much better cook than I am electrician. Check my thread with "nickblake" - I think he probably has made a good point about the separate circuits.

 

[charlhu]

An excellent suggestion but it has its flaws

The Salad solution may only be a partial solution

Who is to say the meat eaters in the family will accept this
A deep roast in a suitable oven exceeds the taste of cold chicken portions I'm sure

I do eat salads but "takeaways" NEVER - and anyway I need to warm my bedtime socks of a cold night,

 

[telectrix]

SALAD... Sandwiches After Localised Automatic Disconnection. SSSimples

 

[charlhu]

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

I have spent a merry Sat morning playing endless rounds of "Trip the RCD" mostly successfully (in getting trips that is). Nevertheless, I have made some progress. I now realize that (correctly) the cooker circuit is not tripped by the RCD - only the two power circuits go out (again correctly).That is to say, in a "RCD trip situation" the oven is working. Repeatedly switching the oven on and off, it seldom tripped (perhaps once in 20 operations. However operating the Cooker Switch almost invariably causes a trip. It can do this both switching "On" or "Off". It does it even if the oven is switched off by the programme selector switch. If I disconnect the ceramic hob from the junction box the problem is there. If I disconnect the oven and have only the hob connected there is no problem operating the cooker switch. That suggests there is an insulation problem with the original oven cable? Since when I switch the cooker switch "On" while the oven switch is "Off" all that comes into play is the cooker circuit trying to feed the oven via its cable? I am at a loss to understand why that would cause an RCD trip on the power circuits when the cooker circuit Live/Neutral amperage differential is not being measured - perhaps some electrician Hercule Poirot will explain it to me!
I would have tried replacing the cable already but it is a two-man job to get the oven out of its housing to access the terminal box and I live alone. Will do it if I am confident that is the cause of the problem.
Anyway, it is in a temporary location under-counter below the hob where the old cooker was postioned. I am remodelling the kitchen and the oven wil go into a tower cabinet on another wall and need its own switched supply installed in a few weeks time. In the light of your comments I won't combine with the hob but have a separate circuit run from the board to an FCU and power socket for the oven. Fortunately, there is one spare space in the board for another MCB.

 

[charlhu]

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

Could you be so kind as to read my latest reply post to "nickblake" and comment thereon?