Voltage on Lighting Circuit

[chalkmycue]

Hello

I am replacing the ceiling pendants in my flat, i have removed the fuse from the ccu and tested for voltage when i test between the permanant live and the neutral it is giving me a 12v reading, the switch live and cpc in any combination are giving a zero reading?

I turned the ccu off using the isolator switch and the reading is now zero which makes me think it wasnt a fault with the volt tester, my thinking is if it has some strange DIY wiring i would be getting a 230v.

Any advice please people.

Thanks Ricky

 

[OilLecky]

It sounds like you have an "induced voltage" i.e. it is coming from a nearby cable either electrostaticaly or magneticaly. This would happen even if you got a piece of cable, not connected to anything at either end and layed it next to some live wiring. A voltage is "induced" in that cable. This is how a radio aerial works and also the method electrical interference in other circuits happens.

When you pulled the fuse only the lighting circuits were "dead", there was still, either current flowing, or an electrical charge in all the other circuits. When you switched off the isolator, all the circuits were dead.

To prove this to yourself, connect a light fitting complete with a lamp (any voltage!) across the suspected live wires and the induced voltage will drop to zero.

( I was once testing a weapons circuit ,with all power off and when I checked for "Nil Volts" on a firing cable I found 90v! It was caused by a nearby radar transmitter! It too could produce a voltage but no power.)

 

[RF Lighting]

I would start to investigate if the voltage was >50V. Anything less is normally just capacitive coupling.

 

[ColJack]

would this tester be a combi tester by chance?

it would read continuity N-E as it's connected at the cutout.. turning off the main switch removes this as it breaks the neutral..