Phase tester lights on screw for switch plate

Metric Tensor

Hi all,

I went to remove a light switch plate today and when my phase tester touched the screw it lit up. The fuse was off at the time. See pic attached.

I will get my electrician as soon as I can in the new year.

Can anyone shed some light on this?

Thanks.

Metric Tensor

OK. Upon some further investigation there appears to be a "leak" in the circuit for the next set of lights. If I knock off the trip switch for that set I no longer get light on my phase tester.

I take it the earth line in the switch is somehow connected to this other circuit.

Not great!

Would appreciate any thoughts.

Thanks.

Bruthal

Phase testers are not great indicators in electrical terms.

However, I would not expect one to light when in contact with a screw as in the photo. It could be that the screw has nicked a wire behind the switch, and/or the switch box is not earthed, if it is a steel box.

It is possible there are 2 separate circuits at a 2 gang switch.

Metric Tensor

Both lights from the two gang switch are dead when the single trip switch is off - is that what you mean by two circuits?

The circuit that caused the light in the tester to go off controls the light in the adjacent room and the boxes are almost back to back.

P.S. Stud wall and all the other back boxes I've opened to date have been metal and have had an earth wire in them.

Metric Tensor

More info:

The switch that's back to back also lights up when the screw is touched. No surprise I suppose.

But ... The other switch on the adjacent circuit, which is the far side of the next room also causes the tester to light up when I touch the screw.

meercat

Metric Tensor wrote: »

More info:

The switch that's back to back also lights up when the screw is touched. No surprise I suppose.

But ... The other switch on the adjacent circuit, which is the far side of the next room also causes the tester to light up when I touch the screw.

I would go with bruthals theory that the earth is not connected somewhere so. You may need a rec to resolve this.

2011

Bruthal is correct. Please take whatever a “phase tester” indicates with a very large pinch of salt. These devices should be banned outright as they can indicate that a live circuit is dead and vice versa.

2011

The OP asked that I would thank those that contributed and say that he has arranged for an electrician to d al with this.