electrical fault puzzle

Where there's a rural ceiling cavity there's always a chance of mice.. ..the dribbly little blighters..

I see what you mean - appropriate spacing might have helped. Given that the incomer is not tripping, that seems to rule out an (earth) fault.

Another possibility is excessive inrush current, which is tripping the type B MCB.

When I did the light conversion I removed all necessary gubbins.. wired direct to the tube holders.

One 6a MBC for the 2 pairs of 6ft led tubes and another MBC for the external security lights.

I still think that you need to look at the inrush current. It may be marginal, and it may be temperature dependent.

This may help.

I bow to folk that understand this stuff. It'd be odd to start happening after 2,3 years of led use and with it happening on each single run of 2 6ft tubes. It's worked during previous heatwaves & Welsh rain

The number of LED lamps fitted are highly unlikely to cause a 6A MCB to trip on inrush. It is also unlkiely to be intermiitent.
I don't think this is a problem that can be diagnosed remotely. The only thing I can think of based on the description is some kinf of intermittent fault in the 4 position switch or it's immediate wiring. I There is not much else that is common to both strings of lights. Damage by rodents or insect infestation is another possibility but unless the two strings share a common cable (3 core and earth is a possibility) or junction box it is still hard to see a common point of failure.

Robert.

Well yes.

If we exclude an (earth) fault and inrush, what is left?

If the cables are T&E in plastic mini-trunking, how could they have been damaged? In any event, surely they can be inspected.

Some readings on the circuits would be useful, but I'm not sure nowadays if an insulation-resistance test can be performed whilst LED lights are connected. Needs an Electrician ideally to assess this.

Other things to check:

- With the incoming power off and everything made safe I would check that the MCB's are properly secured to the busbar in the consumer unit and the circuits are also tightly connected in the MCB's. Might be a loose connection and/or corrosion build-up.

- Swap the inside and security light circuits onto each other's MCB's. If the security lights then start to trip, it could be a faulty MCB.

- Check the connections to each of the light fittings are sound and make good where necessary. See over time if this has sorted the problem. There might be a dodgy connection on both runs of lights. Some of the push-in types of connectors aren't that great in my opinion, if these are what're used, but I doubt this is the issue. Worth checking anyway.

Ed.

Edited By Ed Duffner on 20/09/2023 00:08:22