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

 

[Octopus]

If you suspect the dimmer, simply replace to with a standard switch and see what happens.

 

[HandySparks]

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

Not necessarily. All it indicates is a high resistance fault somewhere in the circuit.
Unless I've missed something, you haven't told us anything to narrow it down to either line or neutral.

 

[Danielwareham]

It's a two gang dimmer and as it was operating one side of the room fine I disregarded it but it could still be damaged on one side and not the other I guess?... so I'll change it over tomorrow quickly to see!

 

[Rockingit]

A firm believer in the principle that normally the most likely explanation is the likely suspect:

Favourite fault with downlights = burnt wiring / connectors
Favourite fault with 12v electronic selv = they fail
Favourite fault with dimmer switches = they fail

Remember also that as most dimmers found nowadays are the Triac type, not just a big resistor, they need a certain amount of load to be stable and a digital test meter is fairly useless at 'testing' them.

 

[HandySparks]

It's a two gang dimmer and as it was operating one side of the room fine I disregarded it but it could still be damaged on one side and not the other I guess?... so I'll change it over tomorrow quickly to see!

Defo worth a try, or even just temporarily bypass the dimmer to check the lights. You'll generally find that each side of a two gang dimmer is a completely separate module, so one side working has no bearing on the other side. In fact, if you have a spare dimmer module of the right size and rating, you can just replace one side.

 

[MarkieSparkie]

Hold on guys what's all this nonsense about faulty dimmers and transformers. Take a step back. OP said the I/P to the transformer primary is only 50V. With transformer disconnected and the feed cable unloaded voltage rises to 240V, but when loaded the voltage drops to 50V again. So the fault appears to be somewhere in the main lighting final circuit.
High on my list of suspects would be a loose connection(s) (L and/or N) in a JB, connection box or ceiling rose joining or extending the feed cable to the main lighting final circuit, as there is no mention of dim lights or problems elsewhere on the final circuit.

 

[Deleted member 9648]

Hold on guys what's all this nonsense about faulty dimmers and transformers. Take a step back. OP said the I/P to the transformer primary is only 50V. With transformer disconnected and the feed cable unloaded voltage rises to 240V, but when loaded the voltage drops to 50V again. So the fault appears to be somewhere in the main lighting final circuit.
High on my list of suspects would be a loose connection(s) (L and/or N) in a JB, connection box or ceiling rose joining or extending the feed cable to the main lighting final circuit, as there is no mention of dim lights or problems elsewhere on the final circuit.

Not sure how that eliminates the dimmer?.....The OP said no other lights on the circuit are affected....it is quite likely only the switched side of the dimmer is subject to the volt drop, which suggests dimmer to me.
As already stated the simplest test is to replace the dimmer for a on/off switch...if the problem persists you can then start testing back with a continuity or voltage tester safe in the knowledge that you are not getting any misleading readings through a dimmer.

 

[Knobhead]

6 tests you need to do:
No load

• L > N
• L > E
• N > E

On load

• L > N
• L > E
• N > E

This will indicate if there’s a high resistance joint and more importantly which leg L or N.

 

[mattmoo1974]

I had this the other week and tracked it down to a netural in a Jb pinched to hard when removing sleeving..
Thus it was semi floating and displayed all the symtoms you have said..

 

[Rockingit]

I think maybe some people are forgetting one little thing, here: The phrase 'it STOPPED working'. ie, it did use to work and then stopped for no explanation.

Unless a cable has been in a jb for so many years it's evolved and grown legs, it's unlikely to be an undisturbed cable suddenly causing problems (assumes it was jointed tight and correctly in the first place, rodents etc granted). So what we have left are components that we know DO fail - filaments and electronics.

 

[HandySparks]

So, what did the fault turn out to be, Danielwareham?