Bathroom light and fan wiring

ianb1965 · 4 Jan 2021

Hi all

We have a three gang switch outside our bathroom. One is for a large illuminated vanity mirror, one for the ceiling light and one for the fan (with overrun timer and an isolator switch above door). But, the fan only works if the main light switch has also been switched on. As the illuminated vanity mirror gives off sufficient light, we never uses the main light. So this means that when we use the bathroom we briefly switch the main light and fan on, then turn them off again so the fan runs on the overrun timer.

I really can’t think of the logic of this. Does this mean that the switched live to the fan isolator switch is wired in series through the main light switch and then the fan switch?

Thanks.

ericmark · 4 Jan 2021

It seems government at one point thought the same, and the original building regulations required the fan could be operated without the lights, however this was dropped.

I remember BAS use to do a circuit diagram of how to wire them using a double pole switch, but with LED lighting anything to save the little extra energy used to be economic to fit would need to cost less than £1, so not going to happen.

Taylortwocities · 4 Jan 2021

It shouldn’t be too difficult to rejig the wiring in the 3 gang switch. Sounds like the fan switch is wired to the switched live side of the lights switch. Just move it to the permanent live.

Depends on how the switch is wired. Post a photo of the wiring if you not sure.

SUNRAY · 4 Jan 2021

ericmark said:
It seems government at one point thought the same, and the original building regulations required the fan could be operated without the lights, however this was dropped.

I remember BAS use to do a circuit diagram of how to wire them using a double pole switch, but with LED lighting anything to save the little extra energy used to be economic to fit would need to cost less than £1, so not going to happen.

Fans are available with more than one SL connexion.

SUNRAY · 4 Jan 2021

If you really want to make a change it's a simple matter to rewire the switch. and there are 2 options:

I don't know your exact wiring details but the switch shown in the thin grey box is basically the same for any format.
As Taylor says the link [highlighted in pink] only needs to be moved for option 1 or for option 2 leave the pink where it is and add another [highlighted in purple] so the fan switch selects which light the fan is controlled by.

Thinking further a third option would be to move the pink onto the mirror switch.

EFLImpudence · 4 Jan 2021

No, my mistake. Sorry - if you have already read it.

SUNRAY · 4 Jan 2021

In case there is confusion over the drawing:

EFLImpudence · 4 Jan 2021

No, I misunderstood. Sorry.

SUNRAY · 4 Jan 2021

EFLImpudence said:
No, I misunderstood. Sorry.

Valid observation. No problem

ianb1965 · 4 Jan 2021

Wow - thanks for quick replies guys. Special thanks to Sunray for the diagrams - I’ll take a photo tomorrow of the switch.

ianb1965 · 7 Jan 2021

Sorry for delay in posting photos. See attached. I’ve labelled the switches. There appears to be a wire running from L1 in the main light switch to Com on the fan switch. Guessing this is the culprit?

Taylortwocities · 7 Jan 2021

Yes, Moove it from L1 on the light switch to Com.

it should really be a brown wire, or have brown sleeve/tape on it.

ianb1965 · 7 Jan 2021

Thanks. There are already two wires in Com, should it take a third?

I can see the L1 on the fan has a brown sleeve on but yes, you’re right, not the other wire.

Taylortwocities · 7 Jan 2021

ianb1965 said:
Thanks. There are already two wires in Com, should it take a third?

Your fan switch only has one wire in it. The black one. Rather than put three wires in the fan COM you can reorder the wires on the three cons so they have two wires each.

So you have a brown wire coming in to the mirror COM, there’s a brown link to the lights COM (as now). Take the other brown wire out snd put it in the Com on the fan switch with the black link wire.

The other end of the black link wire, take it out of the lighting L1 terminal snd put it in the lighting COM terminal.

you should turn have two wires in each COM terminal.

capische?

ianb1965 · 7 Jan 2021

Yes understood thanks.

I was referring to the Com on the light switch which has two wires already. I think your initial post was to link fan Com to light Com thus making three wires in there.

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Bathroom light and fan wiring

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