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RCD tripping on new light cuboard light

Posted: Thu Oct 27, 2011 11:01 am
by IBen

I've wired in a new 'Under cabinet striplight' from Wickes. (Google "")
I've connected it to the downstairs light circuit. A cable goes to a switch were the line from the circuit and the line to the light is connected to the switch. N is directly connected. Cabling all seems okay. When I connect the light (you just plug in the cable, you can link these lights to other lights) everything is fine as well but when I switch on the light at the light directly the RCD switch is triggered.

Now my question is, can it be that the light is simply faulty or could there be something wrong with the cabling? I am not sure whether it is a normal RCD or a RCD circuit breaker. So could the light draw too much current that it needs to be on a 13A circuit (shouldn't really unless it is faulty I guess)?

As it is a lighting circuit earth isn't connected. Only L and N is used.

Thanks for you advice

Re: RCD tripping on new light cuboard light

Posted: Thu Oct 27, 2011 8:13 pm
by sparx
Hi Ben, where did you 'directly' connect the neutral? it must go to the same lighting circuit as the live.
If live taken from switch is the neutral also in a connector in the switch box?

Re: RCD tripping on new light cuboard light

Posted: Thu Oct 27, 2011 8:30 pm
by IBen

I've wired the light directly to the consumer unit (the consumer unit is in a little room under the stairs and there is no light there). So neutral is connected to all the other neutral cables in the consumer unit while live goes to the 'downstairs lighting' circuit.

cable connector
N -------------------------------------|--------------------------------------------N
CU Light
L--------------------------------------/ --------------------------------------------L

Neutral is not connected to the switch (it is just connected with a separate cable connector which is hosted in the the same box as the switch).

I just had a thought. In the consumer unit there seems to be two 'strips' for connecting the neutral. Could that be that they are separated for circuits with different Ampere ratings?

Re: RCD tripping on new light cuboard light

Posted: Thu Oct 27, 2011 8:48 pm
by sparx
Hi again,
the 2 Neutral bars imply a 'split-load' consumer unit with a main switch and an RCD for half the board.
If so normally the sockets etc. would be on the RCD half of the board and lights on the other half.
It is essential that any circuits on the board have both Live & neutral on the same half or the RCD will trip.
eg if main switch on RHS of board all circuits between that and the RCD will not be RCD protected so all those circuit neutrals must go to the RHS Neutral bar.
RCD half is the same ie L&N's from same side.
RCD's work by current balance so if, say Live is from non-RCD side and N is connected to RCD side the RCD will 'see' only the returning current, not balanced against flow current, it will trip as soon as switch turned on. It's not at fault- that's its job!
Look CAREFULLY again.