Cooker appliance earth leakage problem

[Niels Cook]

Anyone help me with this one ?

Recently bought a "new" AEG double oven/grill cooker off ebay, at a small fraction of its retail cost, no gtee/returns, usual risks etc

The catch is, when plugged in/installed as per AEG documentation, my mains RCD keeps outing.

It does this:-

i) When I switch the top oven on ii) After I've switched the grill onto full, & the element has warmed up.

The bottom (fan) oven seems ok.

Taking resistance readings with a digital multimeter between one of the offending element poles and the cooker case/earth (after disconnecting the relevent element poles from any other cooker circuitry) I find that

i) for the grill element it reads 1.5Megohms (when cold - probably leaks more as it heats up, hence errors) and

ii) for the top oven element it's an alarming 0.5 Megohms.

For the fan oven it was about 2 megohms.

I noticed that for my previous Ariston cooker - soon to be ebayed (??!!??) - the earth leakage resistance was higher than the meter could register.

What would one expect a new element, correctly fitted (not wired in) to read in terms of earth leakage ?

I don't want to buy & fit another & have the same problem.

Is my RCD over-sensitive ?

I read somewhere that cookers are notorious for high earth leakage.

The cooker had previously been supplied to a customer (I think) & returned without any signs of use, utensils pristine & bagged up. The cooker looks like it's been handled heavily in it's short life, dents to externals, minor cosmetic issues etc.

Any comments, aside from the obvious "back to ebay" ones would be welcome!

NGCook

[Bob Eager]

They are... the elements get damp if not used, which exacerbates the problem.

Try temporary connection to a non RCD protected circuit, turn it on for an hour or two and then try again.

[Dave Plowman (News)]

If they use mineral insulated elements, this can be true.

If you've isolated the faulty one, change it for a new one.

IMHO, the fact you have an RCD in circuit wouldn't be a reason to get a refund from an auction purchase unless it specifically said it could pass this test.

I've got a split load CU and the oven isn't RCD protected - there's no real reason why it should be.

[richard]

Indeed, it's just asking for trouble, why would you normally have the oven or hob on an rcd?

[Andrew Gabriel]

I can't remember off-hand what the allowed resistance is in the PAT test guidelines, but the guidelines accept that such elements may be out of spec when cold, and allow you to get them to operating temperature and dry out before making the measurement.

Also, the measurement should be done with a 500VDC source; a multimeter will give you a different reading in most cases. (0.5 Megohms is only 0.5mA which isn't enough to trip an RCD.)

Not from any evidence you have provided.

That's why they aren't normally put on RCD circuits, and because they don't justify it on safety grounds. Check the circuit earth is up to spec though.

[Peter]

Why would you have anything on the RCD then ?

Peter

[Andy Wade]

Class I heating appliances: 300 kohm insulation resistance or a leakage current of 0.75 mA per kW (5 mA max.) if using the touch current method.

[richard]

there's

The rcd is to protect a person from death by electrocution. Protection against electrocution from a faulty fixed appliance such as an oven is by earthing the case of the oven and equipotential bonding in the surroundings, leading to the operation of the protective device while keeping fault potentials to earth at a safe level. An Rcd is more important when feeding socket outlets for portable stuff - more likely that a person is gripping the equipment in the first place, more likely that flexes etc will be damaged and more likely to be outside any equipotential zone. But I bow to Andrew Gabriel's wisdom on this matter and stand to be corrected. Rich

[Peter]

but the oven may be connected to a socket outlet on a flex ? Plus isint it more likely to get electrocuted in an earthed bonded zone ? The oven may be within reach of water taps and sink etc which are bonded.

Peter

[Christian McArdle]

Yes, you just need to run off the RCD for a few hours to dry out the element. If you don't have a suitable socket, (such as a non-RCD fridge freezer socket), you could always try it at a mates house.

I would never suggest that you plug it in with the earth connection disconnected for a few hours whilst sitting on an insulated surface (i.e. cardboard box or lino). Not unless you knew what you were doing, anyway, and knew some basic safety rules, like not touching the thing, keeping the family out of the room and disconnecting any gas supply.

Christian.

[Telboy Smith]

That?s what I do, & I?m dangerously underqualified to do these things but hey if your hungry LOL!

Joking aside, everytime our fan oven is cleaned as soon as it?s switched on it trips the RCD in our house. As the oven is built in there?s no way I was going to remove it to try it on non-RCD wiring (maters House) All I have done to get round this is to disconnect the earth wire & switch on the oven for 5 minutes, after which the earth was reconnected & the oven behaves itself, as it should.

But as Christian said I couldn?t advise you to do the same. :-)