RCD tripping when switching oven isolator off

[streamer]

Hi all.
I was called to a house recently where the occupier reported that when they turned the oven isolator off the RCD would trip.
So I tried it and that's exactly what happened. There was nothing switched on on the oven at the time. When the oven is on it works fine.
It is an integrated oven on a dedicated 16 amp circuit. Circuit tested fine in all respects and a ramp test on RCD showed it tripping at 24 mA.
They have to turn the isolator off when not using the oven as they have a son with learning difficulties who sometimes turns the controls on the front of th oven.
Any ideas what the cause might be?
Thanks.

 

[Bobster]

Beama talk about 'Double pole switching within the fixed wiring is known to produce a strange phenomenon whereby switching OFF a double pole switch supplied through an RCD can cause the RCD to trip.' in their RCD Handbook.

So there must be some substances to it.

The only thing I can think of, is it causing some from of capacitive spike in the cable.

 

[marconi]

Re #14: The sequence of switching of the line and neutral does affect the changes of potential differences of the line and neutral conductors with respect to earth - and because of this there is the possibility of transient current flows through the line and neutral conductors distributed capacitance to earth which does create a differential current through the RCD. Plot out the changes of potentials/currents for the equivalent circuit and you will see what happens - which is why in earthed neutral systems single phase DP switches are make N first break N last - so N conductors remains at earth potential - ie do not momentarily jump up to Line potential then down to zero to avoid nuisance tripping of RCDs.

 

[Bobster]

Re #14: The sequence of switching of the line and neutral does affect the changes of potential differences of the line and neutral conductors with respect to earth - and because of this there is the possibility of transient current flows through the line and neutral conductors distributed capacitance to earth which does create a differential current through the RCD. Plot out the changes of potentials/currents for the equivalent circuit and you will see what happens - which is why in earthed neutral systems single phase DP switches are make N first break N last - so N conductors remains at earth potential - ie do not momentarily jump up to Line potential then down to zero to avoid nuisance tripping of RCDs.

Yes, as soon as I stopped an actually thought about it, I realized what could happen.

 

[Dustydazzler]

Had this on a board change I did a while ago.
Customer reported rcd tripping when they turned the cooker off.
I must say this was the first time I have come across this particular problem