Background:
My 1950's house rewired in 2005 to 16th edition. Supply is TN-S.
There are 4 ring finals all protected by a single 30mA RCD. There is a cooker radial in 10mm which feeds a DP isolater (no neon, no socket), and then connects to the cooker which is a dual fuel one, protected by 20A MCB (The 10mm cable was for future proofing). Cooker is not on RCD.
Problem:
Occasionally (maybe 1 time in 10), turning *off* the oven trips the RCD. Seems to happen more if the oven has been on for a long time. It has done this for a few years. The main oven element was recently replaced, and that has not made the fault go away. Also, the trip happens irrespective of whether the thermostat is on or off at the moment you turn off the oven (there's a neon light on the front panel of the cooker showing demand). (Actually there are two fans in the cooker - the fan over circulation fan, and then a chassis cooling fan that is separately controlled by a chassis thermostat)
I'm not an electrician, but do have a background in electronics. I am absolutely stumped by the problem - I can't come up with a single plausible theory that could explain this behaviour.
What would be the best strategy for diagnosing the problem? Is it more likely to be a wiring fault or an appliance fault?
My hunch is that it's something to do with the fan unit on the oven, rather than the element, and some sort of transient due to the inductive load of the fan motor. But it's not a very good hunch.
I can borrow a megger. Wondering if it would be useful to disconnect and test the oven itself. I'm not going to get involved with the house wiring though. But I would be keen to prove it's the oven, or eliminate the oven, before calling someone in to test the wiring.
My 1950's house rewired in 2005 to 16th edition. Supply is TN-S.
There are 4 ring finals all protected by a single 30mA RCD. There is a cooker radial in 10mm which feeds a DP isolater (no neon, no socket), and then connects to the cooker which is a dual fuel one, protected by 20A MCB (The 10mm cable was for future proofing). Cooker is not on RCD.
Problem:
Occasionally (maybe 1 time in 10), turning *off* the oven trips the RCD. Seems to happen more if the oven has been on for a long time. It has done this for a few years. The main oven element was recently replaced, and that has not made the fault go away. Also, the trip happens irrespective of whether the thermostat is on or off at the moment you turn off the oven (there's a neon light on the front panel of the cooker showing demand). (Actually there are two fans in the cooker - the fan over circulation fan, and then a chassis cooling fan that is separately controlled by a chassis thermostat)
I'm not an electrician, but do have a background in electronics. I am absolutely stumped by the problem - I can't come up with a single plausible theory that could explain this behaviour.
What would be the best strategy for diagnosing the problem? Is it more likely to be a wiring fault or an appliance fault?
My hunch is that it's something to do with the fan unit on the oven, rather than the element, and some sort of transient due to the inductive load of the fan motor. But it's not a very good hunch.
I can borrow a megger. Wondering if it would be useful to disconnect and test the oven itself. I'm not going to get involved with the house wiring though. But I would be keen to prove it's the oven, or eliminate the oven, before calling someone in to test the wiring.
