That is very strange. Turning on either set of lights causing an over-current trip implies a common fault or fault load before the switch just under the trip point. Neither of these has an obvious cause. It would require knowledge of the exact wiring arrangement right down to the connection methods used.
What type and rating of lights?
What rating circuit breaker?
What brand of switches etc?

The next step as an electrician would be some measurements, insulation resistance and load current and a detailed inspection..

Robert.

hI If the celing lamps are flurecent then that would be where i would start to look. If one of the chokes has a short to earth the fault could be neuteral to earth. I would disconect each row and check them one at a time till you find the row then check the fittings on that row.

David

I suspect the roof is leaking, or maybe condensation. The ceiling is common to both lights, and should be dry, but isn't. Have a look inside the light fittings for signs of damp.

How long does a shed roof last? Shallow pitch and flat roofs have notoriously short lives. My felt garden shed roof lasts between 10 and 15 years.

Dave

If you have undone the switches and the fault has gone I would start there.

If wired with twin & earth has green sleeve been use on the bare earth in the switch box ? Noel.

If the felt is leaking, (ten years is about the life for felt ) replace it with EPDM rubber.

Rubber $ Roofs (just a happy cutomer) have a calculator on their website. You fill in the dimensioms, and decide what trims you want. It calculates what is needed.

Ordered in the aftrenoon, delivered 0800 next day.

Ample rubber, adhesive, trims, and ring shank nails. (Make sure that you start putting them in where they should be. They are VERY difficult to remove )

When the job is finished, use a Stanley knife to remove the excess rubber (If you are like me; keep it, useful for other small jobs )

Neat, seasmless, and long lasting. We've had an EPDM roof on the garage for 30 years without leaks; hence the choice for the workshop.

Howard  Typos galore!

Edited By Howard Lewis on 19/09/2023 14:39:27

(off topic) First pic made me laugh I'm afraid, having read many posts asking for advice as to how to shift lathes, milling machines etc – you obviously had that part of setting up well thought out!

Other thoughts:

Don't take this the wrong way, but were the LED batons a quality make or cheap as chips? One of their power supplies might be ageing prematurely, causing odd currents to flow in odd places, e.g. to earth.

Ditto the light switch – quality make, or cheapest ? Perhaps a bad connection developed in the switch contacts which cleared when you unscrewed the switch plate to check the wiring. Maybe there is a fracture in one of the wires, but held together in contact by the insulation.

The light in my inherited small garage just will not work reliably. I have had the (Old MK) socket in pieces and cleaned the switch contacts with fibreglass cleaning pen and switch cleaner spray, ditto the 13A plug and pin and socket contacts, but the bloody light just will not work reliably. It is at the bottom of my current to-do list though. Rapid current on/offs between faulty contacts can trip a breaker, as can an incandescent bulb when its filament breaks. Sounds like you might have cleared a fault in the switch ?

Ditto the MCBs in your cons unit; quality or cheapest?

Final thought; has your shed or house installation lost its earth ?

When you converted to led tubes, did you remove the chokes and control gear from the lights, or did you fit the tubes that can be run with the chokes left in? If you did that could well be the problem, and also you will save very little money if the chokes are left in circuit. I think the problem is within the lamps but we do need to know if it is tripping a 6A mcb or an RCD.

Phil

I had what sounds to be the same problem tag end of last year on a the kitchen light circuit comprising a two way switched double running to a triple switch with the third one connected as an independent single way for the pantry light..

Several other lights on that MCB as it was the one handling all my downstairs lights. More on the RCD of course, I have four for the house. Minimum safe number in my view. Methodical checking got it down to being the kitchen circuits. Both switches checked individually. Fault fell off. Back next day! Naughty words and re-check everything.

Fault went away after doing the kitchen circuits and hasn't, so far, come back. All wiring and connections were good all the time.

Clive

Edited By Clive Foster on 19/09/2023 19:59:08

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.

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.