Lighting circuit trips RCD but not MCB, can’t find E-N fault

[Rarbur]

Long shot but thought I’d try, have a lighting circuit that trips the RCD as soon as the neutral touches the neutral bar for said RCD. Bypass that and it works fine just on an MCB so would think earth-neutral fault, but doing an IR test between N and E shows as a pass (>99M ohm). So unsure of what to do, any suggestions would he great.

 

[pc1966]

Do you have more than one RCD / neutral bar?

It could be on the wrong one. Also background, has this developed as a fault and you now find that isolating/replacing the neutral in its old position explains things, or did you do some work and now it is having trouble?

 

[Rarbur]

Do you have more than one RCD / neutral bar?

It could be on the wrong one. Also background, has this developed as a fault and you now find that isolating/replacing the neutral in its old position explains things, or did you do some work and now it is having trouble?

There are multiple RCD’s but have traced the neutral and made sure it is on the right bar. The fault has spontaneously happened, client has had no issues up until now and no electrical work has been done recently.

 

[James]

It may be that you have a N to N fault.
if there is a link from one N bar to the other being generated by a mistake or fault between circuits it could cause the issues you are having.

 

[Pittockc]

Hi all, I’m a Melb based homeowner who has a similar issue.

TLDR: How to fault ID - new RCD trips lighting circuit - motion sensor Poss culprit?
Longer version

Solar installer upgraded MCB from ceramic-wire fuses to RCDs.
Ever since then an outdoor lighting circuit (which has motion sensing and runs PAR floods as well as std bayonet fitting) now trips the RCD on the lighting circuit instantly.
Have been looking at water ingress to fittings but all clean and clear - but thinking movement sensor failure may be the issue?
Old fuse never blew, so unlikely a load issue. Also suspect that one light fitting is actually powered from both the problem circuit and another circuit.
1970s home.
Thnx for any advice.

 

[Rabaraba]

Do you have more than one RCD / neutral bar?

It could be on the wrong one. Also background, has this developed as a fault and you now find that isolating/replacing the neutral in its old position explains things, or did you do some work and now it is having trouble?

That's the likely fault

 

[newfutile]

take all the neutrals out of all the neural bars (mark them first) puts wagos on each one and power up the offending circuit,any neutrals connected though a load will now become live, i use this technique to upgrade mcbs to rcbos