Cooker socket causes main RCD to trip

[deutscheparts]

I have changed my cooker socket twice in the last two years, as the first 2 were dodgy from Wickes, and overheated !
I have a plain white one on there at the moment and it is wired up and working fine, but when I put the screws in to hold it to the metal backplate, as soon as the screw makes contact, the RCD trips out.
I can't understand what could be causing this.
Any help appreciated, don't really want socket detached from wall for too long

 

[Taylortwocities]

Probably the fixing screw is a little too long and it is trapping one of the wires behind it in the box.

Firstly TURN OFF THE POWER
Then remove the front panel and look carefully at the cables inside.
Move all wires away from the edges where the screws are and check to see if there are any bare wires due to damage from the screws. If so you should repair the damage before putting it all back together again.

EDIT: Another possibility is that the wires entering the back box do not have rubber grommets and one of the wires (neutral probably) is in contact with the back box. When you put the fixing screw in you will be effectively earthing the back box and the RCD will trip.
Look at the cables coming into the box, you'll possibly find a bare wire

Do turn off the power when touching this, the neutral is a LIVE conductor and the back box may be connected to it!

Do let me know what u find.

 

[cheesepuff]

you said as soon as the screw makes contact, it cuts out. have you auctually turned off the power for it in the CU or fuse box?

 

[deutscheparts]

I found out this was the problem after fitting the new socket fascia and refitting it all with the power off at the fuse box, but as soon as I switched on the main breaker it would trip out.
I gradually worked my way around the sockets I had changed until I found that the trip would not go off if the cooker fascia was unscrewed from the metal box.
But, as soon as I went to screw the fascia back on, the RCD would trip out literally as soon as the screw made contact with the tab in the wall box, it didn't even start to push the box back.
I've just checked the metal case and it does not cause my electrical screwdriver to light up - does this mean anything?
I'm not sure about the grommet in the box, is it possible that one of the cables is touching the case? Would this cause the problem I've described?
Thanks again, I've not struggled with wiring jobs before, but I can't work this one out.

 

[Steve]

If you've connected all your earth wires to the fascia terminal, and there is a short on a phase conductor to the back box, then when the screw touches the backbox and the facsia's earthed surround, there is a path to earth.

BE VERY CAREFUL - it COULD be a live conductor that is shorting, causing the backbox to be live until you touch with that screw. Use a multimeter to be sure, not a neon screwdriver.

 

[Taylortwocities]

Why dont you read my posts??, I already told you all that....

PS, put that neon screwdriver in the bin.

 

[Steve]

Why dont you read my posts??, I already told you all that....

Not really, you didn't mention that for this situation to be realised, the face plate would be earthed, but not the backbox!

 

[deutscheparts]

I've just had another look at this and it appears that the metal backplate is not earthed as the green / yellow cables that come out of the thick cooker supply cable are only attached to the fascia, and not to the backplate.
There is a terminal on the backplate for an earth, but it is not connected.
Bloody old houses, every simple little job turns into a nightmare.

 

[Taylortwocities]

But the back box does not need to be earthed if one of the fixing lugs is fixed.
If you earth the back box with the fault you have then the RCD will always trip. Lets fix the fault you have first otherwise all of the circuits fed by the RCD will be off.

Did you find anything when you looked at the cable entry points?