Turning a shower fan on with a dimmer switch

[rstark]

Hi

I am installing spotlights in my batchroom which will be controlled by a nice IQ dimmer switch I have which will be installed outside in the hall.

I will also be installing a shower extractor fan (with a timed overun).

Ideally, what I want is the fan to turn on (not control its speed or any such nonsence) when the dimmer is turned on, in any fashion. Then I will also install the a 3 pole isolator to overide the fan.

This would be very easy if I wasn't using a dimmer switch, simply running the switched live from the light and a permenant live/neutral to the fan. How do I acheive the same when the dimmer will be droping the voltage of the switched live?

Many Thanks
Rob

 

[ricicle]

Unless the dimmer has a permanent full voltage output in addition to the dimmed one you won't be able to trigger the fan from it.
You will have to put the fan on it's own switch or have it triggered by a PIR if you always need it to come on.
Or the other option is a grid dimmer in a two gang plate with a normal switch which triggers the fan and powers the dimmer.

 

[Taylortwocities]

Unless the dimmer has a permanent full voltage output in addition to the dimmed one you won't be able to trigger the fan from it.
You will have to put the fan on it's own switch or have it triggered by a PIR if you always need it to come on.
Or the other option is a grid dimmer in a two gang plate with a normal switch which triggers the fan and powers the dimmer.

Well, I am not so sure about that.

I have installed lots of bathroom extractor fans triggered from the switched live that comes from a dimmer switch.

I have never had a problem.

 

[sparkybird]

Yes but if the lights are switched on in a 'dimmed' position, then the fan won't be getting enough voltage and will eventually give up the ghost...

You can get dimmers which have a dual output (not sure if this is the right term), ie when the lights are switched on it triggers the fan at full power. Perhaps a search of the internet will though something up

 

[JohnW2]

Yes but if the lights are switched on in a 'dimmed' position, then the fan won't be getting enough voltage and will eventually give up the ghost...

The design of most/all fan timer modules I've seen is such that that I would have thought that almost any voltage (and any waveform) ought to trigger it (capacative/inductive coupling from other circuits, or even lightning, has been known to do it). However ....

You can get dimmers which have a dual output (not sure if this is the right term), ie when the lights are switched on it triggers the fan at full power. Perhaps a search of the internet will though something up

If such an animal, presumably designed for this very purpose, exists, then that would obviously be the thing to use, thereby eliminating any doubts. It certainly ought to be very easy for the manufacturers to implement (basically just one extra terminal) since I presume that the switching is in the 230V feed to the dimmer electronics. However, the wiring of the circuit would then become a bit more complicated (since the fan obviously could not get its S/L from the light), probably requiring an additional cable.

Kind Regards, John

 

[sparkybird]

John - the fan get it's s'l from the light switch (ie before it's dimmed but after it's switched on IYKWIM), so yes, the 3 core to the fan would need to come from the switch not the light

 

[JohnW2]

John - the fan get it's s'l from the light switch (ie before it's dimmed but after it's switched on IYKWIM), so yes, the 3 core to the fan would need to come from the switch not the light

Exactly. However,as I said, I suspect that TTC is right in saying that the dimmed output will usually work fine.

Kind Regards, John

 

[ban-all-sheds]

I am installing spotlights in my batchroom

If you are having more of these than the number of lights you currently have, then apart from wondering what needing more says about the suitability of them, are you aware that the work is notifiable, and you need to apply for Building Regulations approval?

If the lights are recessed, what's above the bathroom? If it's a loft, or a flat roof, have you thought about the problems with insulation and moisture resistance?

You can't just remove insulation where the lights are, as that will cause Part L problems, create unpleasant cold draughts and, over time, lead to dirty marks on the ceiling.

You need to put an enclosure (build or buy) over the lights to allow insulation to be reinstated. It needs to be big enough to provide the clearance the maker specifies. And it must be sealed to the ceiling to stop warm moist air getting in there or you risk condensation, and that leads to rot. Not much fun, and another Building Regulations contravention.

• http://www.nhbc.co.uk/NHBCPublicati...ical/StandardsExtra/filedownload,16553,en.pdf
  
  
• Pre-formed cap to seal downlights: http://www.aico.co.uk/downlights-in-loft-space-what-to-fit.html (It's NOT a firehood....)
  
  
• IET article on installing downlighters safely

Basically if you do not have access from above it becomes very difficult to install recessed lights where you need to seal them off.

If the ceiling is a fire compartment boundary then you'll need to use fire rated lights.

which will be controlled by a nice IQ dimmer switch

Note that if you are using halogen lamps then dimming them will shorten their lives.