Gas Oven blowing RCD....

[Andy1971]

Hi, new member here, but not new to DIY by a long shot.

Bit of an embarrassing one this, given I am an Engineer of over 30yrs, the answer should be obvious but here goes....

I've recently replaced my old gas oven, which had piezo or battery ignition. The new model has electric ignition and a lamp in the oven (massive novelty factor for me being able to see things cooking after all these years).

When the installation guys came with the new cooker, as soon as they plugged it in the circuit breakier (32A kitchen ring) blew. Nothing else blows this circuit. They made arrangements for a replacement, and a few days later the replacement (a Flavel Milano G50) was delivered....aaaand, same result.

Ok, my diagnosis so far :-
1. Nothing else trips this ring.
2. If I plug the cooker into a different circuit, it's fine and works ok.
3. To clarify, the oven, grill and hob are gas, only the lamp and iginition circuit are electric. It is plugged in on a 32A plug.
4. I have done a con-check across the LNE into the back of the cooker, there are no shorts between L-E, N-E, or L-N.
5. If you just plug the oven in, with the socket switched off, it blows the MCB.
6. I have removed all other devices from this circuit, same result (so it's not overloaded).
7. If I plug the cooker in to any socket on this ring, I get the same result.
8. I have checked all sockets on the ring, all appear ok, no pinched wires etc.
9. To sum up, this cooker only does this, on one circuit, and nothing else on the circuit causes this.

Any ideas before I call a sparky in?

Cheers,

Andy

 

[bernardgreen]

Incorrectly wired socket could be the problem. Has the socket been used for anything else other than the oven ?

 

[Andy1971]

Hi Bernard, yes the socket has been used for a lot of other appliances with no problem at all.

 

[JohnD]

You say "32A plug"
What colour is it?

Or do you mean something else?

You also say it trips the MCB. And the RCD. Which is it?

Is the kitchen floor concrete?

Does the cooker have metal feet or other conductive parts in contact with the floor, wall, pipes, drainer, other appliance? Is the gas connection to the cooker metal or plastic?

 

[Andy1971]

Yeah sorry, it's actually an RCBO.

So, it's a standard 13A plug, going into the kitchen ring main, protected by a 32A RCBO.

It's no excuse, but I was writing my OP in a hurry.....

 

[JohnD]

Does the CH boiler connect to the same circuit?

 

[Andy1971]

Hi, no the CH boiler is on a separate circuit

 

[Alec_t]

I have done a con-check across the LNE into the back of the cooker, there are no shorts between L-E, N-E, or L-N

Was that a DC meter con check? Just a long shot, but perhaps there is a fat suppressor capacitor associated with the N-E wires of the ignition circuit and the initial charge current for the cap is enough to trip the RCB.
Are the LNE terminals in the cooker going to the correct pins of the plug?
Can you disconnect the ignition circuit temporarily to see if the fault persists?
If the socket is wired correctly but the RCB trips even when the socket is switched off, then logically the socket switch is faulty or there is current passing between N and E in the oven or its plug/wiring.

 

[Andy1971]

Hi Alec, the capacitor theory is a good one, and given it being an ignition circuit, quite feasible.
The LNE of the cooker are wired correctly with the plug.
The circuit trips regardless of which socket it is plugged into around the room, which rules out a faulty switch.
It seems strange that it runs fine on my other 32A circuit.
I've removed the lamp, that makes no difference, so maybe it is the ignition. Or maybe the replacement cooker was also faulty? Even so, it still works on that other circuit, and everything else plugged into the offending circuit works just fine.

 

[EFLImpudence]

Is the other circuit also on an RCCB or RCBO?

 

[Andy1971]

Hi, all circuits on this CU are on RCBO's, and the RCBO for the other ring main is identical to the one that blows on the one in question.

Many thanks,

 

[ericmark]

I would first off say cooker faulty, but just one question, does the cooker instructions stipulate type of RCD, all my RCBO's are type AC but some equipment asks for type A or better.

I did have some scales delivered once which had a filter that caused excessive earth leakage returned to supplier and then came back minus the filter, @Alec_t has likely hit on the problem, but not really your problem, the BS7671.2008 does limit the leakage to 3.5 mA when using a plug 543.7.1.1 don't know if that has changed with 2018 version, but good reason to reject anything which has over a 3.5 mA leakage unless connected to the fixed wiring or to socket outlet to BS EN 60309-2 which is not the number covering a 13A socket. Even with BS EN 60309-2 it is limited to 10 mA.