electrical fault puzzle

My shed was purpose built circa 10yrs ago. Low dwarf wall and insulated concrete floor, stud work with insulation, vapour barrier and uovc cladding, light weight faux steel tiles and ply lined with double glazed uovc doors and windows. In other words dry.

Professionally wired with 60a incoming line and sub consumer unit. Breakers fir each row of wall sockets, one breaker shared between both runs if ceiling lights and fourth breaker for external security lights .

There's a 4 gang light switch one for each ceiling run and one for each external light..the originals could be switched to stay on and override the movement detectors and toners. This floods have long since been changed to simple led security floods without that override.

Some months ago the inside lighting breaker was tripping whenever either ceiling light set was switched on. At the time I had enough other stuff going on and left it be.

With the darker evenings I figured I'd better sort it and opened up the light switches expecting to find a short. Everything in their looks very neat and solid. Before starting to look for problems in both ceiling runs I tried the lights again and they now work . Multiple goes on the switches and no problem.

Ok so for the moment I just use it but any ideas for an explanation? Insects got in the consumer unit? Temperature change with time of year?

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.

Tired breaker?

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

A fault on one set of lights would not cause the breaker to trip when the other set was turned on.
A Erth -neutral fault wont trip a circuit breaker. It will trip a residual current device but the OP said it ripped the lighting CB with no mention of a RCD. A RCBO is a possibility on a modern installation but it's highly unlikely a RCBO was fitted to a lighting circuit 10 years ago.

Robert.

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

Like good custard - The plot thickens ! I take it we are talking MCBs ? Not RCDs? A fault that is nolonger there is going to be hard to find ! LED lights can be troublesome but both sets ? MCBs and RCDs can cause odd problems, easy, to spot with the right gear. Assuming you have MCBs can you swap another of the same value ?

As Robert has said, leakage and load, A weak or worn MCB that was only just holding and then dropped, on reset it is now holding properly ? Then your into more obscure, mouse or other animal chews wiring, electrocuted, the carcass has now desicated and reistance has risen. Dampness, though that seems unlikely in view of what you have told us. Good luck. Noel.

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

Hi Pgk, we might need some more info to have a shot at finding a root cause.

- What type of wiring was used to power the faulty circuits? PVC? MICC?

- Are the internal lights LED or another type?

- What type of circuit breaker is used on the lighting, simple overload or do they include fault to earth protection as well?

- Any idea of the power consumption of the number of lights connected to each circuit breaker?

- Is there any other equipment connected into the lighting circuits?

Ed.

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

I'm with you Dave. It's dried out. People always suggest the complicated stuff first.

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

This is an old pic of my shed shortly after completion. Roof pitch quite decent and clad in some galvanised steel sheet tiling that has cosmetic brown grit on its surface. The tiles interlock quite robustly. There is no sign of damp on the shed ceiling which is flat inside.i.e cannot see the internal pitch. Again this is insulated ply sheeting.
Consumer unit is a main 60ARCD with 4 MCB's the lighting circuit NIDCB06

Some 3-4 years ago I converted the 6ft fluorescents to take LED tubes.

Again an old picture from my album but you can see ceiling type and light arrangement. Back then a pair of fluorescents each side (now LED) and the whole shed doshed out in white emulsion. I'd have expected any damp to show up well.

I won't try and guess what the wiring insulation is - looks like ordinary domestic stuff to me and yes the earth bundle in the switch gang is sheathed properly.

(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!

It is not uncommon for a fault to blow itself clear. I would as said above take the covers off each light & inspect for anything that looks like it was trapped or catching anywhere. Also as said water ingress somewhere that has now dried out.

Steve.

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 ?

You haven't specified the type of "breaker". Is the relevant one an RCBO or MCB; and what is the type and current rating please?

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

Yes he has " Consumer unit is a main 60ARCD with 4 MCB's the lighting circuit NIDCB06 "

So RCD on input and 6A MCB feeding four switched light circuits. My understanding is that the fault WAS if EITHER of the two internal light circuits were switched on the 6A MCB tripped.

Robert.

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