Where is the 90v coming from?

[haskey]

Whilst swapping out a security light for another one I noticed that the voltage across the live and neutral was over 300 volts so I started to investigate the 6way junction box feeding it.

The junction box feeds three security lights. The cable to one of those lights has four cores. When the 230v supply is feed to the red and black core 90v is returned on the yellow core. I tried looking at the connection at the light end but I can only see the red and black connected and no sign of the yellow.

Any ideas what could be happening? Where is the 90v coming from?

Thanks in advance.

 

[RF Lighting]

What instrument are you measuring the 300V with?

 

[ban-all-sheds]

When the 230v supply is feed to the red and black core 90v is returned on the yellow core.

Get hold of a 110V lamp and connect it between yellow and a neutral.

I predict it won't even glow, and that if you were to measure the voltage then you'd find it was about zero.

Any ideas what could be happening? Where is the 90v coming from?

This?

 

[Spark123]

Get hold of a 110V lamp and connect it between yellow and a neutral.

I predict it won't even glow, and that if you were to measure the voltage then you'd find it was about zero.

What if it is a switch live return from a PIR which incidentally operates when he connects the lamp?

 

[ban-all-sheds]

Why would it operate when he connects the lamp but not operate when he connects a voltmeter?

 

[Spark123]

Maybe somebody could walk infront of the PIR, maybe it is connected to a switch and someone could operate it. Without knowing the ins and outs of it I certainly would not connect a 110v lamp into a 240v system.
Connect a 240v lamp and measure the volts across it is one method I may use.

 

[ban-all-sheds]

Hmm - I see your point.

I was coming at it from the angle of showing that there aren't 90 "real" volts there (you know what I mean) - you'd expect a 110V lamp to light with 90V across it - not necessarily a 240V one, so when it doesn't light up you've demonstrated that the voltage has collapsed.

If you just want to show voltage collapsing when measured use a moving coil voltmeter and forget fiddling with lamps....

 

[haskey]

Thanks for your answers guys. I originally only measured the voltage using an electronic multimeter. I've not measured the current and it could well be that the voltage collapses as soon as anything is put across it.

I need to find out where the yellow cable disappears to at the other end.