Oven tripping RCD intermittently.

[yakheart]

Our oven intermittently causes the RCD to trip - the oven worked without a fault for many months, but recently it plays up most times it is used, with the RCD tripping every few minutes.

About a year ago, I had the same problem and it went away when I took out and refitted the element. (I was going to replace the element, but the one I had bought but didn't have an earth lead.) This may have been a coincidence, but I assumed at the time the that re-installing the element had fixed a loose wire.

The oven is now playing up again and refitting the element hasn't helped. An electrician previously advised me (by phone) to replace the oven, but I am worried that I could replace the oven and still have a fault in the house wiring and it seems difficult to find an electrician willing to take on the job to diagnose the fault.

Any ideas?

Also, the oven shares its RCD with other circuits, including the ring main sockets. Should it have its own RCD?

 

[jj4091]

Disconnect the element & insulate the wires, if it still trips the rcd when you switch on then you have another problem in the oven or wiring although I very much doubt it. It is very common for faulty elements to trip the rcd so I think replacing that would be the first step if you do not have a megga to test the element insulation. It does not need to be on a separate rcd

 

[yakheart]

Thanks for the really quick reply.

I'll try disconnecting it and insulating the wires.

The oven doesn't trip the RCD as soon as it is switched on. It will run for a couple of minutes and trip it, then run for a couple of minutes and trip it again. Which probably backs up the idea that it is a problem in the element that is affected by it heating up.

So, running the fan etc without the element will be a useful test and won't cost anything to try. Replacing the element would also be the next best step after that, thanks.

 

[yakheart]

Looking for a replacement, and I hit the problem I had a year ago.

Replacement elements only seem to have two connections, but the one in the oven has three and the oven has an earth lead. This includes elements advertised as genuine original manufacturer's parts.

Would it be safe to use an element with no earth if the oven has an earth lead? What do I do with the spare lead - wrapping it up with insulating tape sounds like a bad idea?

 

[EFLImpudence]

It must have a CPC (earth) connected and the burnt attaching screws may be ineffective.

Are you sure it's not just the picture?
Can you post a link?

 

[flameport]

Would it be safe to use an element with no earth if the oven has an earth lead?

No. Are you sure it is the correct element?

I have replaced 100s of cooker elements, and while some do only have 2 connections, that is because so did the original one.

Never yet had a replacement part which had 2 connections where the original had 3.

 

[yakheart]

Thanks again for being so quick to reply.

I have taken out the element, insulated the leads and the oven is running, without the element, without tripping the RCD. So, either the problem is the element, or something that happens to the oven when it heats up.

The oven is a NEFF U1420 and I have posted snap of the information plate which has these details
E-Nr U1420N0GB/01 FD 7902
B-AP54-8 195.911081

View media item 67855
and a photo of the element terminals
View media item 67854
and a photo of the element part number EG0 20.29559.000
View media item 67858
Here is a link to a typical advert for an element for a NEFF U1420 oven...
http://www.ransomspares.co.uk/parts...atible-neff-fan-oven-element-2300w/120674.htm

No earth connection that I can see on the replacement element. (The watermark makes it a bit difficult to see, but I think that the element in the photo has only two elements.)

Also, that link is for a 2300W element, but the existing element is stamped 2400W. I have submitted a question to that supplier on their website about this, but it is the same everywhere I have looked e.g.
http://www.amazon.co.uk/Neff-U1420N0GB-2300-Watt-Element/dp/3020613272
http://www.4neff.co.uk/cooker-oven/...6&path=600196&refine=element&model_ref=403219

The oven is quite old, I should say. About 16 years old, actually. Could it be that the wiring has changed? I haven't seen anything on any on-line retailer saying that the parts only fit ovens after a certain date.

 

[EFLImpudence]

From the link -

In some case the original element was fitted with an earth tag, however this, according to the Bosch technical handbook, is no longer required. Any existing earth wire should be isolated and fastened out of harms way.

Not ideal for the sake of a small tag.

You must make sure the fixing screws make a good contact between the element and the carcass.

 

[yakheart]

OK, dumb of me not to read the page properly.

Next dumb question. How do I isolate the earth lead and safely fasten it away?

Is it enough to wrap the end of the lead in high temperature tape like this http://www.amazon.co.uk/Kapton-Tape...2192745&sr=1-1&keywords=high+temperature+tape and tuck it out of the road?

 

[EFLImpudence]

How do I isolate the earth lead and safely fasten it away?

If there is still a plastic cover over the connector, I wouldn't bother with any tape.
You only have to stop it touching a live or neutral wires.
It doesn't matter if it touches the carcass, that's where it is suposed to be.

I would tie it to another earth wire or similar.

 

[yakheart]

Here is what it looks like (the other two are still insulated with normal electrical tape). Two leads going in to a big metal terminal, no plastic cap.

View media item 67870
What should I insulate it with that isn't going to give me nightmares about it catching fire?

 

[EFLImpudence]

Ah. I was thinking you were in the back of the oven.

What about trapping it between the back and the element?
As I said, it doesn't matter if it touches the metalwork but you don't want it waving about and comming into contact with either of the terminals.

It really is a bit naff of Neff.

 

[knowall]

Ceramic terminal block ?

Regards,

NA

 

[Astra99]

If you really do want to replace the earth connection, two options:

1. Buy a "stationary male" Lucar connector from your local auto-shop and use one of the element fixing screws to secure it.
2. Cut off the Lucar connector on the earth lead, replace it with a ring-terminal (supplied by your local auto shop) and use one of the fixing screws.

If the existing fixing screws are corroded, replace them, again, you local auto-shop will be able to supply.

 

[JohnW2]

... If the existing fixing screws are corroded, replace them, again, you local auto-shop will be able to supply.

I would imagine that (if there is not going to be an explicit earth connection) probably even more important than the corrosion of the screws is that the metalwork of the oven which comes in contact with the element flange (and held in place by the screws) should be carefully cleaned, since that probably represents much more of the electrical contact area than do the screws themselves.

Kind Regards, John