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In article ,
(Niels Cook) writes:
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 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.)

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

Is my RCD over-sensitive ?

Not from any evidence you have provided.

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

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.

--
Andrew Gabriel