RCBO tripping after bathroom works – N–E fault suspected

[Bambino85]

Hi all,


I was called to a job where the downstairs lighting RCBO (B6) is tripping. It started happening after bathroom works were done.


Here's what I've checked so far:

Disconnected all light fittings in bathroom, kitchen, and shaver socket → still tripping.
Tried moving the conductors to the adjacent RCBO → tripped constantly.
Put them back on the original RCBO → it sometimes holds, sometimes trips.
With the circuit fully isolated (L & N off the RCBO), tested with Martindale:
L–E: no continuity
L–N: no continuity
N–E: continuity present

So there's definitely a neutral–earth fault somewhere. The fittings I tested/removed don't show the issue, so it looks like it may be in the fixed wiring or a leg I haven't opened yet (living room/reception/other room).

 

[prestigious-iceberg77]

Hi all,


I was called to a job where the downstairs lighting RCBO (B6) is tripping. It started happening after bathroom works were done.


Here's what I've checked so far:

Disconnected all light fittings in bathroom, kitchen, and shaver socket → still tripping.
Tried moving the conductors to the adjacent RCBO → tripped constantly.
Put them back on the original RCBO → it sometimes holds, sometimes trips.
With the circuit fully isolated (L & N off the RCBO), tested with Martindale:
L–E: no continuity
L–N: no continuity
N–E: continuity present

So there's definitely a neutral–earth fault somewhere. The fittings I tested/removed don't show the issue, so it looks like it may be in the fixed wiring or a leg I haven't opened yet (living room/reception/other room).

You're on the right track checking for N–E continuity with the circuit isolated. A neutral touching earth anywhere downstream will trip the RCBO even if the lights are off. Since it started after bathroom work, I'd go back and check for any junction boxes or cable splices that might've been disturbed or added behind tile or drywall. If the fault isn't at a fitting, it could be in a buried joint or a cable nicked during installation. Did they install any new fixtures or move anything that might've shifted existing wiring?

 

[c0narti$t]

Hi all,


I was called to a job where the downstairs lighting RCBO (B6) is tripping. It started happening after bathroom works were done.


Here's what I've checked so far:

Disconnected all light fittings in bathroom, kitchen, and shaver socket → still tripping.
Tried moving the conductors to the adjacent RCBO → tripped constantly.
Put them back on the original RCBO → it sometimes holds, sometimes trips.
With the circuit fully isolated (L & N off the RCBO), tested with Martindale:
L–E: no continuity
L–N: no continuity
N–E: continuity present

So there's definitely a neutral–earth fault somewhere. The fittings I tested/removed don't show the issue, so it looks like it may be in the fixed wiring or a leg I haven't opened yet (living room/reception/other room).

Have you tried splitting the circuit down into sections and insulation testing each leg separately to see where the fault shows up?

If I am not mistaken, the neutral from the bathroom circuit usually gets tied into another neutral bar or shared with a different circuit. This is the reason for the RCBO to trip intermittently.

 

[VoltagexV]

Hi all,


I was called to a job where the downstairs lighting RCBO (B6) is tripping. It started happening after bathroom works were done.


Here's what I've checked so far:

Disconnected all light fittings in bathroom, kitchen, and shaver socket → still tripping.
Tried moving the conductors to the adjacent RCBO → tripped constantly.
Put them back on the original RCBO → it sometimes holds, sometimes trips.
With the circuit fully isolated (L & N off the RCBO), tested with Martindale:
L–E: no continuity
L–N: no continuity
N–E: continuity present

So there's definitely a neutral–earth fault somewhere. The fittings I tested/removed don't show the issue, so it looks like it may be in the fixed wiring or a leg I haven't opened yet (living room/reception/other room).

I'm with @prestigious-iceberg77. It was good you did the N-E continuity test and confirmed the problem. An RCBO is built to trip exactly for that, even when the lights are off, because current is finding an alternative path back to the source via Earth. The fact it's intermittent suggests a marginal or high-resistance fault. I'd also retrace your bathroom work and look where the fixed wiring was disturbed or damaged. Section the circuit to make it more manageable. Go to the first junction past the consumer unit, disconnect the Neutral that feeds the rest of the circuit, and re-test N-E at the board. If the continuity is gone, the fault is downstream. Then keep moving, disconnecting sections of the Neutral wire until the test comes clear. That'll isolate the exact run of cable that needs repair!!