messed up lighting circuit issue

[jed,da,sparx]

hi guys new to the site
got a problem with a circuit at a property im working on

description

council kitchen circuits rewire
db- 10way main switch rcbos previously installed

problem - 1 x lighting circuit on mcb due to it tripping the rcbo ( last electricians left the rcbo in ccu cupboard, as they couldn't work out issue and left it on mcb )

at first i thought the issue was a borrowed neutral from the other lighting circuit ( because when i removed the neutral from the neutral bar the lights were still on ( i know working live, slap my wrists )
then i turn the power off and checked continuity across the circuits neutral and other neutrals in db -
no continuity
this has led me to believe that the circuit is using the cpc for path back for live
i checked earth to neutral continuity on that circuit and it belled out
i then check it across all earths in d.b ( disconnected ) am im getting continuity between them all even when disconnected from met (e.g new cooker circuit cpc and main earth both not connected in met + even belling out on gas pipe)

im was think someone has screwed through a cable and its touching it all together , but this would be the most unlucky fixing ever made or luckiest as it hasn't hit the lives

anyway hope i have given enough detail on this and maybe someone else has come across an issue like this , coz i am completly stumpped

 

[ImpededLoop]

From what you've described, carrying out the dead tests on the offending lighting circuit should reveal the fault. The insulation resistance test will be the most valuable here.

 

[jed,da,sparx]

From what you've described, carrying out the dead tests on the offending lighting circuit should reveal the fault. The insulation resistance test will be the most valuable here.

Thanks for your reply

I know the insulation resistance between the earth and neutral on the lighting circuit is bad
( due to not being able to get to all connections as they are blind corness roses ect ) I will be rewiring the lighting circuit anyway but my issue was why are all the earths belling out together even though they are disconnected from m.e.t

And was wondering if anyone else had come across this situation

Thanks again anyway

 

[J.C.E]

is it tncs?
parallel paths

 

[Octopus]

I think you need to detail the tests you have done and the actual results.

Then we might have some suggestions.

 

[amlu]

some wiring may be run in metal conduits in the wall, with earthing at various points ( back-boxes, ceiling roses, etc).

 

[Richard Burns]

If you have gas and water then the cooker cpc could be connected to the gas pipes, the boiler cpc connected to the water and gas pipes, if the boiler is on the socket circuit then the sockets are connected to the water and gas pipes via the boiler, an electric shower may be connected to the water pipes, if there is supplementary bonding in the bathroom then the lights, shower, any heaters etc are connected to the water pipes.
Then pretty much all cpcs are connected via the water/gas pipes.

 

[marc8]

Hello Jed,da,sparx

Most RCBO units are single pole devices so when you switch off the RCBO you could still see continuity across the Neutrals on the RCBO'S. you say that you disconnected the Neutral & lights stayed on did you then take out each RCBO Neutral cable on the consumer unit (with RCBO turned OFF) main Neutral Bar as if you did not then just turning another RCBO off being single pole will still allow the lights to work through another RCBO if you have a borrowed Neutral, I would check this first & then maybe if there was a borrowed Neutral check the up to down lighting circuit as most Neutrals are borrowed at this point.
but I could be wrong but worth a try before you rewire the whole circuit.
unsure at this point also that if you had a borrowed Neutral that a lighting circuit on a MCB with a borrowed Neutral from another RCBO if this is the case would not trip that RCBO but then stranger things have happened.
more detail would be nice also

 

[PEG]

Hi dude,you have said the lights remained functioning with the neutral removed,and that the n/e IR is poor...your answer is there.hone: