Outside Lights trip RCD

[McLaren]

Hi All,
I was wondering if anyone could help me with a recent problem I’ve had on a job. About 5 months ago I installed about 5 outdoor soffit lights from switch inside. All worked perfectly and customer was happy. I’ve recently been called back to the job as the outdoor lights have been tripping the RCD. I have carried out all Insulation Resistance tests on all legs of the circuits as well as continuity and they all test perfect however it is whenever the switch live twin and earth cable is live even without the load connected it trips the RCD. I have run a temporary cable from the switch to first light bypassing what I believe to be the faulty switch live cable and it all works with no tripping. I know that sort of answers my own question but I am a bit baffled as to how the cable from switch to first light can test perfectly however clearly isn’t . Sorry for the length of this and any help on clearing this up would be massively appreciated, really bugging me , thank you

 

[haptism]

Maybe damp/water

 

[robd]

Have you caught one of the switch wires so the fault is only there when you screw the box back and it's not there when the switch is off the wall?

 

[buzzlightyear]

The only way of sorting the fault out is end to end testing from the mains to the switch and from their onwards .

 

[Kidsolo]

Are you testing from both ends of the cable? maybe open circuit in one direction and shorted from other direction.... due to rodents chewing it

 

[McLaren]

Thanks for replies. I have tested cable from fuse board to switch ( Insulation resistance and r1 + r2, r1 + rn) and is all perfect and then from switch to first lighting point in Wagos and tests perfect however the rcd will stay on with just the feed cable live but as soon as switch live cable goes in without the load connected it is tripping it. I have bypassed the switch with Wagos and there is no damage to any cables at switch point. I’m puzzled because surely if cable was damp at all it would show on IR Test. Im going to have to get another cable out there I think just really baffles me. Perhaps if something has slightly nicked the live conductor somewhere or the neutral and is not causing it to go down the cpc or neutral perhaps it still causes the imbalance therefore tripping RCD ? Thanks everyone for your help

 

[Wilko]

Hi - any chance that switched L has been joined somewhere? If you can bypass the cable and it removes the trip and if the cable is not faulty, then I’m thinking some other load has been connected to it and is returning using a different N, which then trips the RCD.

 

[McLaren]

Hi - any chance that switched L has been joined somewhere? If you can bypass the cable and it removes the trip and if the cable is not faulty, then I’m thinking some other load has been connected to it and is returning using a different N, which then trips the RCD.

That’s good thinking , cable was run direct and the only bit of work since has been air con unit screwed back on wall however not really where cable was run . Would a Nick in live conductor but not crossing to cpc or neutral have the potential to create enough of an inbalance to trip the RCD. Although I can clearly see a new cable will fix the problem my mind won’t really rest now lol ???

 

[Wilko]

If you’re there and have the patience, I’d dis the new air con circuit L and N and just see if that changes anything with your light.

 

[haptism]

when the IR test is being done was the CPC still connected (continuously) back to the CU ? You could have leakage from L or N through the building fabric to true earth, this wont be picked up if IR test is done on S/L CPC at switch position if the CPC is disconnected. And could be only evident now due to the weather

 

[Davisonp]

I was going to suggest the same as Haptism. A fault between live on the switch cable, and an alternate path to earth, meaning the cable tests OK but there is still a low IR between live and the MET.

 

[McLaren]

when the IR test is being done was the CPC still connected (continuously) back to the CU ? You could have leakage from L or N through the building fabric to true earth, this wont be picked up if IR test is done on S/L CPC at switch position if the CPC is disconnected. And could be only evident now due to the weather

thank you both , this actually seems like it could be the answer as the soffit is aluminium itself and forms part of the metal roof structure ... perhaps somewhere somehow this is the problem ? thanks

 

[dmxtothemax]

Could be a small pin hole in the cable and moisture has gotten in