78volts ?

[craig]

Hi folks,

Can anyone shed some light on this ? I have 5 amp sockets around a room switched from a 2 gang switch at the door. 1 switch for the center light, the other for the 5amp sockets. When the sockets are on theres 240v between L-N and L-E when i swich off theres 78v between L-N and L-E. At the centre light theres a 7 or 8 volts on showing on my Fluke. All the fittings are MK. Tried another room with the same set up and got about 31v at the 5amp sockets ? All the bonding is done, incomming gas and water.Loop tests are all ok. The circuits are all RCBO's. Its a joint box system for the lights. Why the voltage ???

Thanks in advance.

 

[m4tty]

It not induced voltage is it?

 

[Notsosmart]

I would measure the voltages via a wander lead connected to either the MET or a stake to establish exactly where the fault lies. I suspect an earth fault but you may have some switching of neutrals.

 

[SirKit Breaker]

I would measure the voltages via a wander lead connected to either the MET or a stake to establish exactly where the fault lies. I suspect an earth fault but you may have some switching of neutrals.

I would go with that as well. Induced voltage of 7 volts or even 31 I can understand, but 70 plus is a bit high for induction at 240v.

 

[craig]

If I switch off all the RCBO'S bar the one supplying the circuit the voltage is still there, leave all the RCBO'S on bar the one supplying the circuit the voltage disappears ? I cant figure this one, I wired it myself and the only thing I can come up with is the main run of cables notched into the joist under the floorboards is causing some kind of induction ?? as it is a busy run, but I have seen much busier. But with the other RCBO'S off that writes off that theory. Also on the neutral aspect, N-E is 0volts.

 

[Mark_Burgess]

The next thing to do is swap the RCBO with another to rule out a knackered RCBO.

 

[Notsosmart]

If I switch off all the RCBO'S bar the one supplying the circuit the voltage is still there, leave all the RCBO'S on bar the one supplying the circuit the voltage disappears ? I cant figure this one, I wired it myself and the only thing I can come up with is the main run of cables notched into the joist under the floorboards is causing some kind of induction ?? But with the other RCBO'S off that writes off that theory.

Correct; Induction is highly unlikely where would the current be induced from? (I'm assuming you have conducted an IR test)

Also on the neutral aspect, N-E is 0volts.

You would expect this as they are tied together (especially on T-N-C-S) What happens when you disconnect the neutral from the board? (please be careful)

 

[greeny]

What happens with the socket figures when you switch the centre light on/off or remove the lamp/s and then take readings with the sockets on and off.

In other words try to completely separate the two circuits and see if the symptoms change.
Perhaps the circuits are from different neutrals and somehow they are cross connected.
You might even be able to carefully try the two ccts without earths,
I hope you understand what I am getting at. Good luck