Lights RCBO keeps tripping randomly

[sparkler]

I have an issue with a home lighting circuit 6A RCBO provides power to 13 bulbs which randomly keeps tripping, when I say randomly it keeps tripping with no switches or even bulbs being attached to the circuit. Even trips when other appliances that are not on that lighting circuit are not being turned on or off.

The fusebox was replaced 2 years ago with RCBOs. The wiring is old however a condition report was issued as a pass at the time the fusebox was replaced. The ground floor and upstairs lighting are on a single 6A RCBO with borrowed neutral, this has worked fine until now.

During a insulation resistance test there is a low reading on the ground floor lighting however still a pass.

The electrician and I did the following scenario/tests:

1. Replaced lighting 6A RCBO - RCBO trips randomly within minutes or few hours
2. No bulbs attached and no light switches pressed - RCBO trips randomly within minutes or few hours
3. Bulbs attached no light switches pressed - RCBO trips randomly within minutes or few hours

What are thoughts on the possible root cause/issue?

Could the ground floor lighting wiring insulation have become damaged/degraded?


Thank You in advanced.

 

[DefyG]

Dont like the sound of a borrowed neutral but if been working ok for 2 years unlikely to be that.

Are there any external fittings as with amount of rain lately, ingress of water could be a cause.

The wiring could have deteriorated but unlikely in my view unless disturbed recently.

How 'Low' a reading on insulation test? If lower than 2Mohms (1Mohm min requirement) it should have been investigated and initially categorised as 'FI' on the EICR (as should the borrowed N) and shouldn't have been signed off as Satisfactory.

 

[timhoward]

Exactly my thoughts too:

Are there any external fittings as with amount of rain lately, ingress of water could be a cause.

How 'Low' a reading on insulation test?

Any recent DIY or lights changed?
Also consider ramp testing the RCBO, or using earth leakage tester to find out how close to tripping it is normally.

 

[James]

Outside light or security light.
full of water giving a N to E fault on that circuit.
slight changes in the N voltage cause current to flow through the N coil of the lighting rcbo and hey presto off it trips.

to test the theory, remove outgoing lives from rcbo. If it still trips randomly then we know there is a current flowing in the N cable that should not be there.

if I am right then I will send you a bill for remote fault finding and diagnostics.
if I am wrong, damn I need to get the crystal ball recalibrated.

 

[sparkler]

DefyG said:

Are there any external fittings as with amount of rain lately, ingress of water could be a cause.
No electrical external/outdoor fittings.

DefyG said:

How 'Low' a reading on insulation test?
Sorry don't have the actual reading to share that was taken, just that electrician said it was a "low reading but still a pass”

Any recent DIY or lights changed?
No recent DIY or lights changes made

 

[DPG]

DefyG said:

Are there any external fittings as with amount of rain lately, ingress of water could be a cause.
No electrical external/outdoor fittings.

DefyG said:

How 'Low' a reading on insulation test?
Sorry don't have the actual reading to share that was taken, just that electrician said it was a "low reading but still a pass”

Any recent DIY or lights changed?
No recent DIY or lights changes made

It's a shame there are no IR figures available.

Was the RCD ramp tested?

 

[Markyd]

IR results should be on the cert

 

[DPG]

IR results should be on the cert

I meant the current figures from the fault finding being done now though.

 

[sparkler]

It's a shame there are no IR figures available.

Was the RCD ramp tested?

Hi, No RCD was not ramp tested. At the time Fusebox was updated to RCBOs in 2021 the reading for both lights upstairs and lights downstairs was following test results section attached.

Thank you