cooker tripping rcd when switched off

[stredwizard]

HI all

I see this has been partially covered before, but I have a different problem

When we first moved into our flat we were skint and were given a cooker with one faulty ring , which I removed the knob for and wired it in, now since the very first time we used it, it works fine but occasionally would trip the rcd when switching the main oven off, we got used to and put it down to the faulty ring.

Anyway we eventually bought another one much more modern all working perfectly Except this one also trips the rcd when switching off the main oven

Now I'm no electrician but I wired these in myself as having done a few over the years

I would live with it but it also knocks out all the sockets (except kitchen) and half the lights,

On the consumer unit if I switch off the other two mcbs that are on the same rcd circuit as the cooker it trips everytime immediately if switch the control knob on and off

Sorry its such a lot of info but is it likely to be a wiring problem or an appliance fault

Thanks
Scott[/list]

 

[Porque223]

One guess would be that the transient (low pass) filter inside the RCD is not working properly.
The response time of this subcircuit is adjustable at the factory and other RCD makers may have made a different tradeoff with response time and safety.

I have heard of GFCIs doing the same thing. I guess the technical term would "transient rejection ratio" or something similar.

 

[PrenticeBoyofDerry]

Does the RCD trip when you turn cooker off at appliance controls or at the isolator switch?
Have you tried disconnecting the cooker from the circuit, then trying the isolator switch?
May rule out some possibilities!
You may have been very unlucky and bought a faulty new appliance, which coincidently trips RCD as did old one !

 

[stredwizard]

Thanks for the replys.... my pal suggested a weak rcd? Have just tried switching the cooker off with the isolator switch and its fine in that way, doesn't trip the rcd and can switch back on and the oven restarts, although the missus reckons the old cooker used to trip even if we switched it off the isolator.

So for the time being I've asked her to switch it off that way and let me know if it does trip out.

So I'm guessing its likely the cooker at fault or the wiring between the isolator and flex outlet or the flex itself?

Thanks
Scott

 

[PrenticeBoyofDerry]

There are number of tests that can be carried out on you installation.
I would test insulation resistances of the circuit and then test trip times and ramp test the RCD.

Is the cooker a plug in one?
Does you consumer unit have dual RCD both with socket outlets on?
If yes to both above questions, run an extension lead from a socket on other RCD to cooker and see if that then trips the other RCD.
If it does I would then be very suspicious of cooker and replace it! I guess it is still under warranty?