Switched live for bathroom fan is live when switch is off

[riverpinn]

My bathroom fan stopped working so I bought a new one. I wired it in but when the bathroom light switch was turned off the fan came on. "I must be dumb" was my first though so out with the meter and let's check the wiring.
It appears that the light switch feeds the lights (of course) and also the switched live circuit that arrives at the double pole switch outside the bathroom. Lights on, volts at the switched circuit on the double pole switch. At the fan the perm. live is "live" but switch live is "dead". If I turn the light switch off then the switched live at the double pole switch is "dead" but the switched live at the fan is now "live". "I must be nuts" was my next thought. In the end I disconnected the feed to the lights and the feed to the fan from the light switch. No lights, no fan. When I touch the two wires together (they were both fed FROM the light switch remember) the fan starts. I am very confused and without taking part of my ceiling down I cannot see the wiring.
Any ideas?

Untitled

• riverpinn
• 27 Dec 2010
• 1

Tim

 

[bernardgreen]

First observation from the diagrams

It is impossible to have 230 volt at one end of a conductor and 0 volts at the other end. Those results would suggest the wire is broken or you have clamped onto insulation at one end and you are measuring at the terminal which inot connected to the wire.

The fan running when the lamp was OFF suggests you have got the wiring at the fan wrong. I think you may have connected permanent live to the fan's neutral and the fan's live to the switched live. This would created a circuit from live through the fan---switched live wire----filament of lamp---- neutral. The lamp filament would easily pass enough current for the fan to run apparently normally without the filament becoming hot enough to glow.

If you have mixed up live and neutral at the fan this could explain the "odd" voltages on the switched live as you have not got the same reference for the readings at the fan as you have for the readings elsewhere.

 

[Taylortwocities]

And that isolation switch should be thre pole.
That is disconnecting live, switched live and neutral.

Also, try testing those points again using earth as the reference. If you get different results then you have a faulty, or miswired, neutral.