Lighting circuit fault

[edd_the_cat]

Hi am new to the forum, am a industrial sparky with a need of some advice.

Have a problem with a lighting circuit in my flat, the circuit has 5 light fittings as well as a 12V lighting rail system in the living room. Three of the light fittings are working as required the other two and the lighting rails are not. I found one of the light pendants was a dead short across the fitting so I disconnected all but one of the light pendants, I cannot find the lighting rail transformer to disconnect it. At the Lighting rose of the pendant which I left connected, but which was not working, I got the following readings.

With no lamp in fitting.
P-N 125V
P-E 248V
N-E 55V

With lamp in fitting
P-N 59V
P-E 248V
N-E 175V which fades to 151V

I can see why the light fittings are not creating the potential across lamps which they need to function correctly, but I cannot find the fault that is supplying 55V through the neutral to earth when the lamp is out. Any help would be really greatly appreciated.

 

[telectrix]

classic poor connection neutral or broken neutral. it will be between the last working light and the first faulty one. if you are lucky, it will be at a light. but could be a JB where someone has spurred off.

 

[edd_the_cat]

Thanks I will check all the neutrals I can get to, any advice for hunting JB's in a flat?

 

[sparkshower]

I would break the circuit down (when isolated of course) check continuity of conductors between the last working and first non working light just by shorting ends and checking with a multimeter see what readings you get on what cores etc

 

[telectrix]

beaten to it. either that or use a wander lead on the neutrals. ( a length of single cable will do )

 

[Strima]

any advice for hunting JB's in a flat?

Where ever you think it is then it's not. It will be in the most awkward and inaccessible place going.

 

[ruston]

Where ever you think it is then it's not. It will be in the most awkward and inaccessible place going.

It may be possible they are looped through at the switches. (with a bit of luck in this case). The transformer may be hidden in a cupboard somewhere. If they are converted flats or the older ones you may have a job on your hands if they have been done from above.

 

[telectrix]

just have to work logically. set up a work station, tool box, meter, site radio, some bits if cable, a few beers, then trace fault from a to b to beer, to fault.

 

[edd_the_cat]

Aye have just done a wandering lead test on my neutral, have defiantly lost my neutral between the two sides of the circuit. The neutrals are only looped through one switch. Checked for the transformer everywhere obvious but no luck I bet its tucked up in the roof somewhere, anyway thanks for the help guys, at least the fault is getting narrowed down.