Cooker tripping RCD

23 Feb 2013
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United Kingdom
We have a New World built in cooker with a top oven / grill. The control for the top oven/grill is one switch that when turning on first turns on the top open (with temperature range 80 - 240), then on turning the switch past the 240 setting turns the oven option off and activates first the "half" grill then the full grill.

When using the top oven everything appears fine, it does not trip the RCD.

When using the grill all is OK until switching off, then when the switch reaches about the 120 setting for the top oven the RCD trips.

Is the fault in the oven element, the grill element (which has power supplied when on the oven setting with 150V to outer element and 80V to inner) or elsewhere?

I have swopped the thermostats in the top and bottom ovens and same happens so that seems to rule out the temperature control unit.

If using the top oven so the grill element has not been on full power the RCD does not trip when being turned back past 120

Any help would be appreciated.
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It's usually an element which has failed. I can't work out from your description which one. You are going to have to change at least one anyway, so work out how to disconnect and remove the elements, and start by disconnecting the most suspect one.

It will probably be the one that did not get red-hot. When elements break down, they tend to get damp inside, and getting very hot will dry them out for a while.
If it's RCD or RCBO that is tripping favourite is the element, which one is difficult to tell by your description.
You can check this by removing electrical contacts to elements (isolate circuit and prove dead first) and do a continuity test on them.
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The elements are hygroscopic that is they will attract and absorb water and to get a 100% seal on an element which is being heated and cooled is always a problem.

For this reason it was common at one time to feed the cooker with a non RCD protected supply and since not plugged in this was allowed.

However new rules in 2008 required protection for wires buried in a wall which means not to use a RCD means the use of special cable.

There are ways to dry out the element but on an open forum I will not say how it is done as too easy for danger to result. However I am sure most electricians will know and would help. However likely the fault will return. Where caused by months of storage then worth giving it a go but in most cases there are only two options.

Renew the element or have Ali-tube cable fitted which does not require RCD protection. Clearly changing the element is the cheaper option so likely that's the best option for you.

With rings spills can result in problems with the element, but in an oven the location means far less likely due to simple spill, and more likely that the element is faulty, and what ever you do, the fault will either remain, or return after a very short time.

Using an insulation tester which works with 500 volt you can easy work out which element is at fault. However with a multi-meter where likely no more than 10 volt is used the fault may not be apparent.

You may find a supplier willing to test the element but since I have an insulation tester I have never asked.

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