Lighting fault which I cant explain!

[LlandrilloSpark]

Fellas
Had a call out to a tripping MCB, 6A Starbreaker, the kitchen lights trip the breaker intermit idly.
The lighting arrangement is 5 X 35w LV Halogens on a wire rail, voltage is stepped down via one 210VA transformer, I tested the cable from the switch (looped N) to the transformer L-N, reading was >600Meg, I removed the lamps and tested the L-N on the rail >500 meg, The transformer was replaced last week by a DIY friend so that is new, no trapped conductors in the switch.
Swapped the 6A starbreaker for one I had in the van, tripped again, replaced it with a 16A as its wired in 1.5mm and it has cured the problem, it’s only a GF flat and there are two lighting circuits, I can’t imagine that half the flat can draw more than 6A?.
I’m going to order a 10A as I can’t be sure it’s wired in 1.5mm throughout and also a type C 6A.
I also couldn’t find any high loads on that circuit, like a DIY socket?
Any ideas?!!

 

[telectrix]

a clamp meter would be a good idea. also, there could be an intermittent fault, maybe breaking down when warm?

 

[D Skelton]

Have the problems begun after the transformer was replaced or before?

 

[LlandrilloSpark]

Long before the tranny was replaced

 

[D Skelton]

I'd go with Tel's advice and clamp the circuit. Are there more trannys on the circuit or just that one? What is the total load of that circuit without applying diversity?

 

[LlandrilloSpark]

clampmeter reads about 5.1A with everything on in the flat, i doubt its all lighting, i reckon hidden socket, funny how it holds on a 16A

 

[sparks1973]

yep...my reckoning is there`l be summat else pulled of ov this in there....

 

[D Skelton]

Very strange indeed. I would check that the circuit doesn't supply anything in any other flats. I was once working in a flat, isolated the lot and the kitchen sockets were all still live! They were being supplied from the flat above!

 

[telectrix]

check that the central heating isn't taken off the lighting circuit.

 

[D Skelton]

check that the central heating isn't taken off the lighting circuit.

Good point. Could trip the breaker every time the thermostat calls for more heat?

 

[drew35]

Coincidently at a quite today I noticed they had a frost watch heater connected to the light circuit in their entrance hall, apparently it was put there to keep their shoes warm before they put them on.

 

[Octopus]

Aerial amp, shaver point?