RCD the curse of all electricians.

Lux · Dec 1, 2011

Installed 1 x 40A-30mA rcd on 4 lighting ccts, went around the house switching things on to make sure all was ok, suddenly it started tripping,
disconnected all the ccts apart from the one i was concerned with as that was what was required to be protected, It worked untill i got to the kitchen and switched on the light, tripped the rcd.
Seperated all the neutrals, earths & phase conductors, IR test, was fine up to the kitchen, had some strange readings so left it out and went back down, reset the rcd and now it will only stay in when there is nothing switched on.
I was getting 153 Volts Phase to Earth, 77 volts Neutral to Earth and 230 volts from phase to neutral.
The earth voltage fluctuated by 10 volts with switching of loads.
Does anyone out there have some advice, would be much appreciated.
Have had to connect the house up to just MCB protection at this stage to allow them to see at night, will have to go back next week for the first fix on the bathroom upstairs do Ill remedy the situation then I hope.
Worst case scenario is running a new cct back to the board and isolating what is existing from what i have worked on to ensure my side of things meets the current regs.
Might point out in NZ we dont use ring ccts, one line back to the switch board for each cct.
Cheers

Richard Burns · Dec 1, 2011

With the voltages you are describing to earth it sounds like you have a poor circuit protective conductor / earth connection, depending on where you were measuring. This would need to be resolved, but should not cause the RCD to trip.

The tripping of the RCD sounds like you have a neutral crossed over on to the non RCD side of the consumer unit or possibly a slight connection at a fitting if there are multiple circuits at a switch.
If you do an IR test between the neutral for the RCD side and the neutral for the non RCD side with the neutral supply from the RCD off (assuming CP) and with all breakers and the main DP isolator off these should not be connected.

Lux · Dec 1, 2011

I'll look into it, will do some more research tonight.
Thanks.
If I resolve the problem I let you know what it was,is.

LineProducts · Dec 1, 2011

Could there be an actual fault-I.e. Leak from the circuit? I once had a similar problem and discovered that someone had borrowed neutral for another circuit but if this was the problem it wouldn't switch on. But from what you are describing it's downstream from a switch. When you power up you feed neutral so seems like neutral is leaking somewhere. To check remove all bulbs, etc (as for ir test) and try again, then try switches one at a time.... Adding one bulb will power up neutral....