Got back from work today, switched the kitchen lights on and the circuit breaker tripped. Assuming it was a bulb blowing, I reset the breaker and tried again. Same result. Then took out all six gu10 type bulbs so that there are no bulbs left on the circuit and tried again. Same result.

None of the bulbs are obviously blown. None of the sockets have obvious signs of problems. The other lights on the same circuit all work fine so long as I don’t turn the kitchen light switch on.

I’m a bit stumped. What’s the best way to go about diagnosing the problem?

If you have reached the zenith of your electrical diagnosing capabilities… Get an electrician in?

Could be fault on the neutral side, or possibly earth. Further than that, I wouldn’t like to guess.

If you’ve really removed all the lamps from the circuit, Id then check each GU10 lamp holder and holder connections for damage, then switch for any signs of damage/shorting.

Is it a simple SPST switch? Not a dimmer or anything?

Well that’s the next option if there’s nothing simple I’m missing.

Stoner, that’s the plan but they’re pretty well fixed to the ceiling. It’s on a triple switch (no dimmer) but the other two work fine.

how are they “fixed to the ceiling”? Are they downlighter cans?

They should just pull down – held in by two springs.

Exactly that but painted over and the plaster isn’t the most robust.

are the cans closed bottoms or open?

if he latter then the lamp holder is only held in place by a metal arm that is slotted sideways into the spring, so you can slip it out and pull the bulb holder down through the can and out for inspection.

EDIT:

painted over

lazy bastard 🙂

Not painted by me!

Had a similar problem once, intermittent tripping on the upstairs lighting circuit.

Turns out that the pvc on the live in one of the light switches had been cut as it had been pulled through the steel backbox. Random movement would cause this live to make contact with the backbox and hence cause an earth fault trip.

Isolate at the consumer unit and check behind the switches. If this has happened, you’ll see the carbon residue from the arcing.

If the breaker stays reset until you operate the kitchen switch, and then trips, you have a fault with the switched live from the switch up to the lights. The location of the fault is the next problem. As mentioned earlier start at the switch to see if there is anything obvious behind there, by the sounds of it that is an easier point to get access to. If all is well there it sounds like it might be at one of the light fittings themselves. Assuming you’re using either halogen or LEDS they may be buried in thermal insulation which will not allow heat to be dissipated. Usually the terminations and the cable melt, which could have caused a line to neutral/earth fault. To diagnose this remotely needs an insulation resistance test so have a little look around first. Obviously isolate everything first (and test to ensure it’s dead, don’t assume!).
Hope it helps.
Andy

Reckon I’ve found the location of the fault – one of the lights pops when it trips. Too dark at the moment to do much more so I’ll check more tomorrow but thanks for the suggestions all.