RCD Trips after two minutes ?

Dave1982 · Mar 10, 2011

Hi all.

Can anyone tell me why an RCD would take more than 2 minutes to trip after the main supply circuit has been energised.

Will not reset immediately afterwards but will reset after 3 to 5 minutes of isolating the circuit.

This is with no loads connected. that is all MCB's switched off.

My supply is from a SWA cable connected into a fused switch incorporating a BS3036 60 Amp fuse. The cable run is approx 12mtrs from the meter and cut-out dissapearing into the wall cavity and reappearing upstars of a domestic property converted to an appartment.

Any expert help would be gatefully appreciated.

tony mc · Mar 10, 2011

If your RCD is energised and you disconnect the line conductor and leave the neutrals all connected in the main neutral terminal is what you have done.

Now if the neutral and earth touch it can still cause a imbalance in the trip coil of the RCD and the unit trips.

Also when people decorate and pull socket fronts off to push the wet wallpaper in this can trip the RCD even when the line is off.

Outside lights which have been wired not useing a double pole switch can cause havoc,water slowly gets into fitting and causes earth neutral fault RCD trips and normally in early hours .

Hope this explains.

Dave1982 · Mar 12, 2011

Well guys thank you all for your replies...all been taken on board. I got back to the job and isolated the problem to the kitchen ring. after further investigation and after removing the washing machine from under the worksurface...lo and behold directly beneath the double socket located above the worksurface a plummed in trap screwed to the wall. Didnt need a plum line to see the scrwes were directly in line with the cable run. Cheers again....will be more thorough next timewith my visuals.

telectrix · Mar 12, 2011

don't we just love plumbers and/or DIYers.

tony mc · Mar 12, 2011

Thanks for the update Dave.

pushrod · Mar 12, 2011

Thanks for the info
Must admit to still being a bit confused on this one.
It was taking 2 minutes? for the rcd to trip with all the power on and when all(?) the mcbs were off at the same time it was still tripping in 2 minutes? and you weren't able to reset for a couple of mins either after a trip?

Have you had a chance to see what the screw was doing- was it giving a link between N and cpc?

Were you able to put an earth leakage clamp meter on the Earthing conductor when the installation was off - i have come across strange cases where the installation has been completely isolated and yet there is still a varying current of 20 to 40 mA in the Earth