RCD tripping, lighting circuit.

[MICKYSPARKY]

just changed CU at domestic proprty, re-energised circuits found all cicuits except ground floor lights keeps tripping. after lifting floor boards to inspect wiring noticed first light on cicuit is fluorescent live, neutral earth conections, found the earth was picked up from ring main JB, all lights after were single core live neutral no earth. found that the neutral on this circuit is permanently live, even when i disconnect from the CU, any info please

 

[chloebear]

ks like the favorte old trick of borrowed neutral from another circuit for the lighting. Have they taken the nutral from the downstairs lighting circuit?
Had this before where the stair lights 1x bottom light + 1x top light switched togethersame line cct, but neutrals were h from differenet circuits - makes no difference as far as the old rewireable fuses are concerned - but will never get an RCD to stand up.

 

[MICKYSPARKY]

Thanks chloebear, i will check this today, will let u know the result.

 

[Johnny-G]

If only there was some way of testing circuits before a CU change.

 

[telectrix]

if you disconnect the N from the CU, it WILL be live, due to the fact that all the circuit will be sitting at 240V. looks like you need to do some serious investigation here. linked circuits, bodged up JBs, shared |Neutrals, etc.