Switching/lighting problem

[MarkP]

Hi guys. I went to a property yesterday where the guys have walked off site. The first fix has been completed and the property has been plastered. I've tested everything (IR) and everything appears fine but I've found a problem. In the main bedroom there is a main light and two wall-lights which you can switch on via a pull core. They weren't previously connected in the jb in the loft. On connecting the wall-lights first to the jb in the loft they worked first time but after about 5mins of them been on there was an almighty bang and all the upstairs lights tripped out. I then disconnected them from the jb and u/s lights work fine again. Any of you guys have any ideas what could be the problem?

On past experience when stuff goes with a bang it's normally a short circuit but I can't understand why they'd come on for a bit then go.

 

[Des 56]

I've tested everything (IR)

Earth continuity tests ?

What tripped out, Mcb, Rcd, Rcbo ?

 

[MarkP]

The lighting circuits are on rcbo's.

 

[Des 56]

Has a test for insulation resistance between live and neutral with the pull cord in the on position been done?

Given that you have earth continuity and the insulation test was ok
I agree that a short circuit was likely



If there is a transformer ,is this ok

When connected without the lamp is the circuit holding in

Is there wet/damp plaster behind the fittings

If no, then it may be just the lamp shorting whilst blowing

The insulation and continuity tests should reveal the fault
Partial nail penetration when somebody walks across the floor boards is another I've come across

 

[MarkP]

Has a test for insulation resistance between live and neutral with the pull cord in the on position been done?

Given that you have earth continuity and the insulation test was ok
I agree that a short circuit was likely



If there is a transformer ,is this ok

When connected without the lamp is the circuit holding in

Is there wet/damp plaster behind the fittings

If no, then it may be just the lamp shorting whilst blowing

The insulation and continuity tests should reveal the fault
Partial nail penetration when somebody walks across the floor boards is another I've come across

There isn't a transformer installed. they are just looped with 1.5mm t&e from the jb to one light then another 1.5mm t&e to the other light down the wall and up into the loft. There isn't any sign of mechanical damage and the plaster from what the customer has said was done 4weeks before xmas.

Just can't get my head around it. Last thing I want to do it have to start chasing out again and put new cables in.

 

[jjjinx]

mark, let us no wat it was please mate, try testing again like des said. Might wana try disconnecting the wall lights and seeing if the circuit works fine wivout em, then test the wall light wiring & try block connecting the lights end & connecting again.