Neutral issue me thinks!!!

[Danielwareham]

Having an issue with some downlights. The lights suddenly stopped working and the customer said they had no idea why! The downlights are on a downstairs ring and none of the other lights are effected. So my first thought was a problem with one of the transformers so I disconnected each transformer in turn to see if I could eliminate the one that was causing the problem (only three lights).
Removing each transformer didn't help so I disconnected the rest of the circuit from the first light so there was only one light being feed from the switch wire and fitted a new transformer. Again not working and when I tested the voltage before the transformer and it was only giving 50 volts, removed the transformer and downlight and tested it again and it gave 240 volts!

So whenever I put a demand on the circuit I lose masses of voltage... so I can only think of a broken or badly terminated neutral as the reason??!! Access is a issue in trying to track this neutral down so could I link into another lights neutral from the same ring? No other rooms are affected so this seems a logical solution. I have access for this and I can't think of a reason why it wouldn't work??!!

Suggestion please. Very new and learning. Fine with installing new stuff but fault finding and problems solving I struggle with...

Thanks

 

[philipb]

Hi Daniel,
Its not good practise to feed lights from a ring main,not your doing but if possible it would be best to supply the
lights from the lighting breaker,if you link a lighting nuetral to the downlights you could cause
crossed nuetral to the ring which would trip any rcd.

 

[Danielwareham]

Sorry if I wasn't clear but I'm talking about using a neutral from the exsisting lighting ring not the ring main! This would be ok I take it?

 

[Adam W]

If you start testing the circuit as if it were a new circuit, that should throw up some odd results somewhere along the way which will give you a good indication. Given that the problem is with the downlighters that will give you a starting point.
Try to avoid putting 500v across live and neutral though...

 

[Adam W]

No it's not OK to borrow a neutral. It's OK to pull in a new feed in that's where the problem lies.

 

[philipb]

Yes that will be fine,sorry when you said downstairs ring i thought you meant ring main,
maybe its me but i refer to rings as ring mains and lights as lighting circuits.
you will be fine,sometimes its easier to run a new cable than trying to find
the fault,just remember to disconnect the original cable.

 

[Danielwareham]

Using the exsisting live feed and putting in a new neutral from the downlights to the junction box where the other lights on the same lighting ring run to?

 

[HandySparks]

Again not working and when I tested the voltage before the transformer and it was only giving 50 volts, removed the transformer and downlight and tested it again and it gave 240 volts!

So whenever I put a demand on the circuit I lose masses of voltage... so I can only think of a broken or badly terminated neutral as the reason??!!

If you're measuring the voltage between line and neutral, why do you think that it's a neutral fault? Surely it could just as well be a fault in the line?

 

[HandySparks]

ie, perhaps the fault is in the switch. Is it a dimmer?

 

[Danielwareham]

Doesn't the drop in voltage when the circuits under demand indicate a neutral issue?

 

[GLENNSPARK]

you could seperate section and do an an R1 R2 then an R2 Rn....see if the results are similar (assuming it is t&w)...what size cable is it? 1mm?....1.5....?....

 

[Danielwareham]

It is a dimmer! What's your thinking behind the dimmer switch?

 

[GLENNSPARK]

It is a dimmer! What's your thinking behind the dimmer switch?

Well maybe someone IR tested at 500V through it....

 

[Danielwareham]

T&w 1.5.

 

[Marvo]

As a rule in most UK domestic installations you should always get zero volts if you test between neutral and earth (CPC). If you get a voltage (>1volt) between neutral and earth even when the circuit is live and under load then you have a neutral problem.

A drop in voltage (L-N) could indicate a missing or partially missing live or neutral.