Rcd tripping on downlights

[cliffed]

Been called into a job,electrician who started to find the fault,left & said he couldn’t find the fault,leaving the client running extension leads everywhere for lights,even in the bathroom.
Basically for what ever reason the rcbo trips ,it can be reset but trips again.
It’s a bungalow with joint boxes for the lights,& loads of fibreglass.Ive split the circuit so now half of the lights are on,but kitchen & diner are off.
The M ohm resistance of the faulty cable is L - E,N - E 0.09,L- N 6.90,
No idea why this cable is at fault,managed to get to all lights,they seem ok,not ideally terminated but looks ok.
Later today will try & get to switches & megger as I go along,the baffling thing,is that this fault is happening ,it a nightmare.

 

[Octopus]

You've done well so far, keep gong in a methodical way.

Are there any outside lights?

 

[cliffed]

No they are recessed lights,loads of them,& jointboxes,logically there’s no reasoning for the fault.

 

[Octopus]

Are they lv downlights?

 

[David M]

You've done well so far, keep gong in a methodical way.

Are there any outside lights?

I had exactly this once. I was called out to a house where the RCD kept tripping from the lighting circuit. After a couple of hours testing and searching the home owner decided to mention an old outside light that had "never" worked. The kids had been playing football a while back and had smashed the glass cover. But as the light never worked they just ignored it as it was down the side of an alleyway that they never used. Turned out the supply to the light was still intact and live, a water filled lamp holder was the problem.

 

[telectrix]

try dissing the working part of the circuit. then try feeding the part that is currently dissed.if it works then it may be the MBC part of the RCBO that's tripping on inrush.

 

[rolyberkin]

How many lights on the rcbo are they LV or 240v, do the lights trip on switching or randomly? any signs of rodent damage? have you or the other electrician changed the rcbo? If not what are the RCD test readings? Have you tested Live and Neutral joined together to earth on the insulation test?

 

[Octopus]

If there are only 2 rooms to go .......... disconnect the lights at the switches .......... than add 1 by 1 to see how the IR results change, and if the light buld can be removed you NEED to do this. L&N to cpc isn't a great help in such situations.

 

[Pete999]

How many lights on the rcbo are they LV or 240v, do the lights trip on switching or randomly? any signs of rodent damage? have you or the other electrician changed the rcbo? If not what are the RCD test readings? Have you tested Live and Neutral joined together to earth on the insulation test?

240Volts is LV

 

[rolyberkin]

I didn't expect him to have 11kv lamps in his ceiling but okay 12v or 240v!

 

[buzzlightyear]

look for any nails in the walls near the light switches .

 

[buzzlightyear]

Later today will try & get to switches & megger as I go along,the baffling thing,is that this fault is happening ,it a nightmare.

think of the xmas bonuses for doing the job !

 

[cliffed]

How many lights on the rcbo are they LV or 240v, do the lights trip on switching or randomly? any signs of rodent damage? have you or the other electrician changed the rcbo? If not what are the RCD test readings? Have you tested Live and Neutral joined together to earth on the insulation test?

Rcbo tests fine,they are 230 halogen lights,same results L+N to Earth 0.09.

 

[cliffed]

try dissing the working part of the circuit. then try feeding the part that is currently dissed.if it works then it may be the MBC part of the RCBO that's tripping on inrush.

Yea that’s what I’ve done,half are now working

 

[cliffed]

I had exactly this once. I was called out to a house where the RCD kept tripping from the lighting circuit. After a couple of hours testing and searching the home owner decided to mention an old outside light that had "never" worked. The kids had been playing football a while back and had smashed the glass cover. But as the light never worked they just ignored it as it was down the side of an alleyway that they never used. Turned out the supply to the light was still intact and live, a water filled lamp holder was the problem.

Thanks,no luck there,ex lights are ok.