Bathroom fan signal live wire on a dimmer - okay or not?

[Alla Musica]

Hi all,

I hope you're all enjoying your festive winter.

I'm just imagining ideas myself - but let's assume the following scenario:

As per the British norm, the bathroom lights and fan are on the same switch (on the wall just outside the bathroom). A permanent live powers the fan; a switched live (controlled directly by the light switch) powers the lights and feeds the voltage signal into the fan.

That means, the lights and fan will usually come on simultaneously on being switched on. After the lights are switched off, the fan will overrun for a set amount of time and turn off as well.

At this stage it is impossible to run another switched live from the backbox to the ceiling to separate the fan from the lights without breaking the walls.

Now the question is - if the lights are dimmable, could I put a dimmer on the switched live? I think, as for the switched live into the fan, all it does is sending the signal into the fan and telling it to stay on - does it matter how many volts the fan needs to receive in order to be identified as a signal? More importantly - it is safe or not?

Much appreciated for taking your time!

Very best,
Chris

 

[SPECIAL LOCATION]

As per the British norm, the bathroom lights and fan are on the same switch (on the wall just outside the bathroom). A permanent live powers the fan; a switched live (controlled directly by the light switch) powers the lights and feeds the voltage signal into the fan.


Chris

Not 100% what you describe is actually the norm?
I see many different arrangements...

However re your dimmer question....
without giving it a try to see what happens I don't know?..

However you do need to remembering that it is the light turning off that starts the fan timer...
So the question is how low can you dim the lights for it to still work without the fan thinking the lights are off??

I think I have seen dimmers triggering fans in the past...
But I am also sure I recall various problems with LED's still glowing when turned off due to sharing supplies with a timer fan?

Dimmers and LED's can be a pain in the bum as it is..
Adding a timer fan as well onto the same equation could be just another can of worms..

If you can access the wiring above the ceiling but not down the walls.. could you fit a ceiling mounted motion sensor to trigger the fan, and leave your dimmer just doing the lights??

Or.. leave your switch just for the fan..
and get some smart lights you can dim from a phone App?

 

[Alla Musica]

Not 100% what you describe is actually the norm?

I would assume this is pretty much the norm? This is my 5th year in the UK and, according to my past experiences while visiting my friends' places, the above arrangement (cr. Vent-Axia) is the most common one (though yes with exceptions)...?

However re your dimmer question....
without giving it a try to see what happens I don't know?..

Welp, I don't have such a fan myself - so if anyone out there knows, apparently I then won't have to buy a fan just for the experiment...

So the question is how low can you dim the lights for it to still work without the fan thinking the lights are off??

Yes - I wonder how far I can dim the lights down without activating the overrun timer...

However you do need to remembering that it is the light turning off that starts the fan timer...

Ah, that's interesting - did you mean that normally the signal terminal needs to have a potential of 0V (or almost 0V) for the timer to kick in?

 

[Geoff1946]

The answer could vary between different makes and models of fan, different dimmers and even different lamps.
The technical support people at the fan manufacturer may have helpful advice if you phone them..

 

[Chewbacca]

Ah, that's interesting - did you mean that normally the signal terminal needs to have a potential of 0V (or almost 0V) for the timer to kick in?

I don't think he's right about that, or the fan would not work when you switch the light on. Either way it's probably looking for a 240V pulse.

 

[Bruspark]

The rising edge of the switched live turns the light and the timer supply on
When the switched live falls the timer starts counting and as it does it supplies the fan from the permanent live unit it counts to zero
What happens if the switched live is half way will vary by product

 

[runningpiglet]

I know for a fact that the xpelair DX100T fan worls fine from a dimmer live. Even the lowest dimmer setting where filaments barely glowing (this installation had incandescent lights) was sufficient to trigget the fan and overrun time was same as when triggered by higher dimmer settings.

 

[Alla Musica]

I know for a fact that the xpelair DX100T fan worls fine from a dimmer live. Even the lowest dimmer setting where filaments barely glowing (this installation had incandescent lights) was sufficient to trigget the fan and overrun time was same as when triggered by higher dimmer settings.

Thanks for the real-life example - that's really interesting!