Cooker tripping RCD after element replacement ONLY when the back cover is off

[SaltedMixedNuts]

The cooker is a beko kdc653k. Electricity was off at the board when working with it, obvs.

The main oven element faulted. Any time the oven was turned on at the oven the RCD tripped. The top grill oven and hobs were fine.

I removed the faulty element for inspection - showed signs of damage so I ordered a new one. Replaced the back cover of the cooker (you need to unscrew the element from the back) and put it back in its slot.

Realised that now the RCD trips when the cooker is turned on at the mains. Assumed it was because no main oven element present and thought nothing more of it - the microwave and air fryer would get me by til the replacement element arrived.

Replacement arrives - easy job to install it. With the oven still without the front inside fan cover or the back cover on I figure I'll do a test - flick the main switch and the RCD trips.

Hmmm. I check to make sure I've got the live and neutral connected the right way and I do so I give it another test.

That's when I notice there's a flash when I flick the switch where the main oven lamp is.

I disconnect the live, neutral, and earth from the lamp and this time it's all ok - oven turns on, the fan runs, and after a few seconds I can feel heat from the element. I assume perhaps the new element has knackered the lamp a bit like when you have a faulty bulb on a car and the new one makes another pop. I order a replacement online.

It's not vital so I reassemble the cooker, pop the cooker back cover on, then because it's a new element, I went to run the oven for an hour or so but the RCD trips as soon as I turn it on at the mains.

I remove the back cover and test again - works fine.

I check all the cables - everything is plugged in and secure. The only wires I've touched at the live and neutral for the element and the live, neutral, and earth for the lamp. The lamp is fully disconnected remember.

This time I just screw the back cover on with the top two screws but again the RCD trips when I turn the cooker on at the mains.

Now I don't know what the consequences are for not having the lamp connected and plugged in so I wait for the new lamp assembly to arrive.

I install it, connect the live, neutral, and earth back up - this time the RCD trips regardless of the state of the back cover.

At this point I've reached the limit of my know-how so I call in an electrician and tell him everything above. Takes 2 days to arrive and when he turns up at 5pm he says he isn't actually going to touch it because he won't work on something a novice has touched. I mean I guess it is understandable since it likely adds a lot more variables to his troubleshooting but I told him everything on the phone 2 days prior Big waste of my time.

So basically as it stands

If lamp is connected and back cover is not on - RCD trips

If lamp is connected and back cover is on - RCD trips

If lamp is disconnected and back cover is on - RCD trips.

The only working combination is lamp disconnected and back cover not on.

Any advice? I'm willing to ring another electrician but should I be sparse with the truth and just give him the symptoms rather than a run through of things I've done? I don't want to wait a few days and be disappointed again.

I've checked the wiring from the wall to the power panel on the rear and it's all good - none of that has been tampered with while I replaced the element.

One thing I'm curious about though is this; the only obvious earth wire comes directly from the power panel on the back cover and it only plugs into the lamp. RCD trips if that earth is plugged in.

The wiring inside the oven is multi-coloured and it's not obvious really what's live, neutral, or earth but the earth is clearly yellow and green.

 

[AC Power]

Well, I remove the back cover, use a flashlight to peer into the screw holes....ensure your mounting screws are not piercing a conductor's insulation beneath the chassis!!! If you can't see beneath the screw holes, simply put all the cover's screws back in WITHOUT the cover on.....see if those screws are penetrating a conductor that you can't see!

If you are pinching/piercing the wiring feeding the interior lamp base (E26), the circuit will only hold (ON) when the cover's screws are not installed, and nor is the lamp connected.

 

[piglet11]

Clearly you have a fault that must be rectified before you proceed.

Older consumer units "fuse boxes" had RCDs on the ring circuits (normal sockets), but installers would put the cooker and immersion heater outside the RCD protection.

It doesn't make sense but that's the way it was.

I guess it was because cookers and immersion heaters were considered "leaky" and would cause nuisance tripping.

But all that was doing was covering up earth leakage faults.

Is the lamp Small Edison screw? with Edison screw lamps, the "pip" on the bottom needs to be the live, but even if that were wrong, it might not trip.

You are quite certain it's the RCD and not an MCB? The RCD will have a test button on it, the MCB won't.
The RCD will trip on very small fault currents, say 30-mA, but the MCB goes on it's rated current.

If it worked before, something has clearly happened. It might be nothing to do with the element or lamp.

If you can't pin it down, it's a job for someone with an appliance tester, but my advice is not to tinker too much.