Earth leakage high on oven but no trip?

[Rockomuir]

Morning,
Customer has a intermittent trip which I am trying to locate. 4 circuits on rcd. Two rings , cooker and hob and one I cannot find actually powers anything as yet. Rings test fine and cooker circuit is okay continuity and I/r. I have put my earth leakage clamp on tails and when I go around turning everything on the meter reads between 5-5.4ma all good. When I turn the oven on the meter jumps to 28-30ma for a bit but Trip holds and then settle back down to about 7. I thought I had cracked it but trip held. I did rcd test which was okay and ramp test tripped in 21.3ma. Do ovens normal have high earth leakage to start off with? And should the trip have popped. Obviously while I have been here trip has held.

Thank you

 

[Rockingit]

** This is a guess **

There could be moisture trapped inside the oven somewhere which causes an initial leakage which then literally instantly dries itself out as the element comes on.

Another guess is that it could be some cheap and leaky electronics on a control/clock display panel when it fires up.

However..... the oven could a red herring and I'd strongly advise that you chase down the 'missing' circuit.

 

[timhoward]

I'm suspicious of the oven element. Resistances do change as it gets hot and cold.
Equally if the oven isn't used much condensation/moisture can build up especially this time of year and you are seeing it dry itself out as @Rockingit said. So it might be a red herring.

As it's easier, I'd first IR test the unknown circuit, L+N together to E, 250v first. It might be a N-E fault on that circuit that the oven is pushing more current through.
If that is clear, then I'd test the oven element, you are looking for 20-50 ohms between terminals on continuity, and then IR test each terminal to earth. This can be done in situ if you take the back off, or if element can be removed from front that is sometimes easier but don't hold it during the test

I'm also wondering - with clamp meter on the tails you are measuring the other side of the board too? So the total leakage might not be quite as high as you thought?

 

[Rockomuir]

Hi thanks, I am not convinced it is the oven either. I am trying to locate this circuit but it is a mystery at the moment

 

[timhoward]

Hi thanks, I am not convinced it is the oven either. I am trying to locate this circuit but it is a mystery at the moment

Just disconnect it and IR it L+N > E. It doesn't matter if you can find it or not, at least you can rule it out then. (Old immersion heater is always my first guess)