Do you ever have one off those days where you feel like throwing your tools in a pile & setting them on fire?! Today was one of them. Basically, yesterday I tested an installation before a replacing an ancient fuse board. All IR results were fine apart from the lighting circuit. L-N >299 megaohms, L-E 10 megaohms & N-E >299 megaohms. Turned on lights & it was tripping the RCD. I first thought maybe there was a shared neutral as there's another lighting circuit but I doubled the circuits up & it's still tripping the RCD. Turned off all the lights, turned RCD on & it stayed up, half of the circuit the lights turn on without tripping no problem, half seem to trip the RCD. Next step is to start disconnecting & breaking everything down but it really is going to be a ball ache & take ages as there's so many lights & switches. Any suggestions or recommendations for things to try? I have disconnected all other circuits on RCD so that I know for sure it was the lighting circuit causing the problem.
RCD tripping
- Thread starter Meatpig
- Start date
Sponsored Links
Do you mean you have disconnected all the other conductors - Lines, Neutrals and CPCs?
Any cheapo dimmers on the lighting circuits? (proper oldschool triacs, not LED things). Or (if its a largish place) emergency light charging unit, alarm panel?
Yes.
There is a dimmer now that you mention it but it’s been turned off all the time when lights have tripped.
Sponsored Links
Well worth disconnecting it and retesting to be sure....
Other than splitting the circuit in the middle to find where the fault is and then the faulty half in half again, etc., I don't know.
However, the figures you have obtained should not trip the RCD, so does that mean something happens when you turn on the power?
However, the figures you have obtained should not trip the RCD, so does that mean something happens when you turn on the power?
Any outside lights with PIR sensors, daylight sensors or similar?
Switch all lights off at the switches. Disconnect and link L&N at the board, test IR between those and CPC, with CPC still connected to the earth bar.
If ok, switch on one light only and test again, then repeat with the other lights, only 1 switch on at a time.
Can I ask why leave the cpc connected to the earth bar and not disconnect please?
If the CPC is disconnected from the Earth bar ( and hence no longer connected to Ground ) then resistance checks between Neutral ~ CPC and Live ~ CPC will not discover the stray contact as in this sketch. The word appliance includes cables and wiring as well as equipment.
A cable that has has its insulation damaged / chewed and hence has a path to Ground ( not the CPC ) through damp or moisture is likely to cause the RCD to trip but checks of insulation resistance from Live to CPC and Neutral to PC will be "good".
EDIT... checks of insulation resistance from Live to CPC and Neutral to PC will be "good" as the Ground is not connected to the CPC.
Last edited:
Brilliant thank you
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
