I bought a big secondhand range cooker which has two ovens, one gas and one electric and an electric bbq.

I've wired this on its own radial to a 40A MCB, protected by a 30mA RCD. I can have all electrics on (probably about 10kW in total) and everything runs fine. The only problem is that when the electric oven reaches it set temperature (and switches off the heating elements) it trips the RCD.

Any idea what might cause this?

Seperate from this, there are two rings on 32A MCBs on the RCD, and when I switch one of those MCBs off, the RCD trips after a while. I don't think this has anything to do with the cooker problem as it already exhibited the problem before connecting the cooker. As far as I can see there is no mix up of neutrals or anything like that.

Thanks,

Koen.

The manual for the cooker says that it can be wired to a 32A MCB, so the 10kW was probably a generous estimate. I used 6mm2 for the radial.

It's only the electrical oven that trips the RCD. The bbq or the grill in the gas oven happily switch off when reaching temperature. So far it's tripped every time with the electric oven, but I get shouted at for testing too much (every clock needs resetting in the house for instance). I will megger the cooker to make sure that the problem isn't with the insulation. Not sure if I can emulate the 'temperature reached' state very well though.

About the two ring mains, everything works fine when both MCBS are switched on and the RCD doesn't trip (this has been on for several months now). However I've been working in the kitchen, putting more sockets on one of the ring mains, and when I switch that MCB off, everything is fine (RCD stays on), however when I return a bit later to switch it back on, the RCD has tripped. And this happens every time too.

Thanks a lot for such an extended response already.

Koen.

i would say its triping cos of a thermal fault on the element.
its cooling when switched off and touches the casing of the element i reckon, or the switchgear does.

ss

I estimated the 10 kW, I need to add up all elements to see how much exactly. I hope the cooker manufacturer was right (Britannia, I'd expect them to get things right). Cable run is about 10 metres.

Maybe the delayed RCD is the answer, as a lot of current is suddenly stopped when the oven switches off. I don't think it's the heating elements touching, because the rcd trips exactly when the oven switches off (temperature light goes out). I will test the insulation on it too though.

Koen.

I meant what was the current RATING of the RCD within the CU 60A, 100A. The reason for asking was that as the oven switches off (temp reached) maybe, only MAYBE, then there is a current surge not a differential imbalance of 30mA.

I would probably have fitted the cooker in the non-RCD side anyway and only the final ring circuits, shower etc on the RCD side.

RR

PS. The manufacturers DO get it wrong by the way, numerous instant heating shower makers get it wrong in their installation instructions.

Ref RCD tripping after a time while you are messing extending the ring.

If you short N to E during that time, it will tirp, and i guarentee you are, by cutting the cable, scraping the wall or wall box etc etc.

Why a cooker on the RCD?  What type of eathing is it??  Do you have an 'earth rod' outside??

I have had this problem before with a new cooker, they replaced it, and it worked fine.

I appoligise to all if i am repeating!!

First.  Simple solution to the problem is to do what you should have done in the first place - put the cooker on a non-RCD circuit.  If you'd done it right the first time you'd be blissfully unaware of a slight earth leakage at certain times.

Second - RR - even if it is 10kW, the diversity guidelines produce a load of 20A, or 25A if there's a socket on the CCU, you know that.

So whilst personal preference might be for something sized to cope with the full load, for the manufacturer to suggest 32A is in no way irresponsible.