Strange readings when connecting up wall light

[Tomparry94]

So I'm doing a job and when connecting up a wall light to a single 1.5mm T+E it does not work, there is another wall light that is connected up to another single T+E cable, however this 9one does work.
when testing the cable coming out of the wall when connected into a connector block with no light I get the usual readings, L-N 230v L-E 230v and N-E 0v. Although with the light connected I get the following readings L-N 0v L-E 230 and N-E 230v

Originally I thought it would have been reverse polarity or a junction box in the floor boards not connected up correctly but cant quite get get my head around why the readings change when the light is connected but are as they should be when it is not!!
I have tried swapping the fittings over and they both work but then connected up to this cable they don't! :confused5:

If somebody could shed shone light on the situation that would be greatly appreciated!

 

[uksparks]

If you are getting neutral to earth of 230v you must be connecting it wrong.

 

[uksparks]

If it's correct with nothing connected then when you connect it all if a sudden you have N-E of 230v, surely it's got to do with the way you are connecting it.

 

[telectrix]

or the N has a poor connection somewhere and that is breaking down under load.

 

[uksparks]

I think I'd have to stand there to see it to be honest as if it works on one and bit the other... What happens if you connect the known good light to it?

 

[uksparks]

or the N has a poor connection somewhere and that is breaking down under load.

Im guessing the light is not on possibly so may not have any or minimal load..

 

[ImpededLoop]

or the N has a poor connection somewhere and that is breaking down under load.

Agree with this. Do the wall light cables go to a junction box somewhere? I'd look there if so.

 

[Tomparry94]

Could it be that the neutral is not connected then? Guess that would make sense.
The connections on the wall light are just L-N-E so no chance of connecting it up wrong... Unless I'm colour blind and I just don't know it yet!!

 

[Tomparry94]

They must do yes, I imagine under the floor boards somewhere, this makes complete seance now!

 

[uksparks]

If there's 230v on the end of the wire my money is on what's being connected.

 

[Octopus]

Get your wander lead out and dead check continuity of the 3 cores would be a good place to start!

 

[Tomparry94]

The fitting is fine, I wired it to a plug top to test it, and when swapping around the lights the same problem

 

[Tomparry94]

That would have been the next thing I did, didn't have time to look into it too much! Can't wait to be ripping the floorboards up to find the junction box!!

 

[SJD]

So I'm doing a job and when connecting up a wall light to a single 1.5mm T+E it does not work, there is another wall light that is connected up to another single T+E cable, however this 9one does work.
when testing the cable coming out of the wall when connected into a connector block with no light I get the usual readings, L-N 230v L-E 230v and N-E 0v. Although with the light connected I get the following readings L-N 0v L-E 230 and N-E 230v

The N connection is not a low impedance to the installation N? Once you try to pass any significant current from L to N, the N floats up to 230V. Perhaps the N is not actually N but has something high impedance in series with it (smoke alarm, etc)?

Just to add: if the light used to work once, perhaps something has been changed/added somewhere, it is worth asking. The fault may not be under the floor, it could be at a ceiling rose or smoke alarm housing.

 

[Octopus]

The fitting is fine, I wired it to a plug top to test it, and when swapping around the lights the same problem

Do you know what a wander lead is?

 

[uksparks]

sounds feasible

 

[Octopus]

That would have been the next thing I did, didn't have time to look into it too much! Can't wait to be ripping the floorboards up to find the junction box!!

Why???

 

[Geordie Spark]

They must do yes, I imagine under the floor boards somewhere, this makes complete seance now!

I think I would rather put my trust in some decent test instruments than a clairvoyant.

 

[Tomparry94]

Do you know what a wander lead is?

I know exactly what a wander lead is yes. Why do you ask?

 

[Octopus]

I know exactly what a wander lead is yes. Why do you ask?

So why ignore this step in fault finding and go for the floorboards up idea??