Author Topic: Bathroom fan wiring  (Read 207 times)

Bathroom fan wiring
« on: May 18, 2020, 09:26:32 am »
As part of Miss Ham's bathroom refurb, I replaced the extract fan.

The original xpelaire had two way switch 3&earth cable, of the three wires, one (appeared to be) permanently live, the second appeared to be switched in parallel to the light so the fan went on when the light was switched on and carried on running until the internal humidistat switched off.

Replaced with a pull switch device, two wires, connected to the perm live and neutral.

All seems well, except that when you switch on the fan the (now LED) light  turns on, too.

Can't get my head around the logic of that.

Re: Bathroom fan wiring
« Reply #1 on: May 18, 2020, 09:33:35 am »
Full brightness or dimly? The current flowing to the fan can induce a small voltage in the unconnected switched wire which can be enough to make some LED lights glow.

Re: Bathroom fan wiring
« Reply #2 on: May 18, 2020, 09:53:42 am »
Yeah, hence why I specified LED, although they appear to be full brightness, 3 x about 5W FWIW.

Re: Bathroom fan wiring
« Reply #3 on: May 18, 2020, 11:10:08 am »
One possibility is you’ve somehow got wired the fan in series with the light, with the fan in parallel to the light switch. Does switching the light switch on turn off the fan?

I think either way you need to disconnect everything and definitely identify which wire is which. Assume nothing about the competence of the previous installer.

Re: Bathroom fan wiring
« Reply #4 on: May 18, 2020, 11:23:27 am »
My original assumption was that the sensible option was the  obvious one - that the three cores came from the light feed, with the live as a spur from the live loop, and the other two from the switched live and neutral.

Can't easily get to the wiring and, as it operates, there's no pressing reason to. Next step is to document the various permutations. I've had the meter on the terminals and I'm happy there's 240 and neutral connected.