Electric Oven / Earthing?


Postby Did it myself » Mon Dec 15, 2008 11:13 am

I've just wired my new oven and hob in but when you turn the oven on it runs for a minute or so before it cuts out.... it doesn't trip the RCD.

When checking the consumer unit (replaced a month ago) I noticed that the oven is connected to a 32A MCB and the electric hob is connected to a 40A MCB.

I called the electrician back to check this over and he is adament that there is nothing wrong with the Ampage on the MCB's. He checked all the wiring and checked my hand-work and gave it all a clean bill of health. However the oven continues to run for a minute before cutting out.

The electricians diagnosis was that there is an earth fault on the oven. Its a brand new oven... his explanation was that it could be th "element expanding and touching something" causing it to earth and cut out.

Can anyone comment on this or does it sound like an appliance fault?
(We do have a service engineer coming to take a look too, but I am just weighing up the electricians diagnosis).

Thanks
Last edited by Did it myself on Mon Dec 15, 2008 4:28 pm, edited 1 time in total.
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Postby ericmark » Mon Dec 15, 2008 12:33 pm

You have not said what is tripping out but I will guess RCD.
Ovens have normally mineral insulated elements which are hydroscopic and will absorb moisture when used on a regular basis then any moisture will be driven off with the heat each time it runs but if left in storage for a while you can get too much moisture and it will trip the RCD before it is driven off.
The cure is dangerous while being done and as a result I will not say how on here in case someone copies and forgets to reconnect things after.
But I guess it will be what the electrician will do when he gets there and within half an hour all will be running OK.
With near all supplies in a house being RCD protected maybe they need to re-think on type of element to use in future?
Eric
ericmark

Postby Did it myself » Mon Dec 15, 2008 4:28 pm

Thanks Eric, this is helpful as my electrician did explain about the moisture problem also, which makes me more confident in his explanation. My concern was that he was defending his work and blaming the oven. However, as the oven has been in storage this sounds plausible. The NEFF engineer will sort it i'm sure. I'll let you know what they say. Thanks again.
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Postby ericmark » Mon Dec 15, 2008 8:31 pm

Glad I was able to help. In the past I have powered them from a generator to dry them out i.e. no RCD in circuit and there are other methods as to what the NEFF will do I don't know as although drying out works if left again unused the same could happen again so he may change the element to be on safe side.
Until June this year it was common not to take cooker supply through a RCD and often the cooker manufacturer recommended they were not supplied through a RCD but now there is no longer any way out with most houses. This is because of cable type and root. So we have no option any more, so I would think cooker manufactures will need to modify how they seal the element ends.
Eric
ericmark

Postby Did it myself » Wed Dec 17, 2008 9:27 am

Hi Eric,

The NEFF guy came to look at the oven and it ran without any problems.... typical eh! He thinks that the electrician may have sorted the problem when he checked everything over the other day.... either that, or the oven has had chance to 'dry out' or 'drive the moisture out'.

What we also found out...

We bought the oven as part of a kitchen bay display from MFI. The NEFF guy informed us that the oven, although new/unused, is actually 3 years old and has been used in several kitchen displays... which would be consistent with the theory that the element had got some moisture in it.

Thanks again.... although I may be on here again when it packs in on Christmas day!
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