Could I use this motion sensor to trigger an extractor fan?

[Ian H]

I want to fit a bathroom extractor that’s not connected to the lights or a pull switch.

I want to use the type where the fan motor is a seperate unit rather than built into the grill.

Could I use one of these to trigger it when someone goes into the bathroom?

https://www.astra247.com/mini_pir_s...D2Ch3RbHhIBsprPgM1d_mvlNTOsLesqhoCg9MQAvD_BwE


The fan would be something similar to this:

https://www.toolstation.com/airvent-100mm-mixed-flow-inline-extractor-fan/p70282#full-desc

Thanks.

 

[bernardgreen]

Could I use one of these to trigger it

If you mean that the sensor triggers a timer in the fan then the answer is almost certainly NO

If you mean the timer in the sensor controls how long the fan runs after movement stops then it might work. It depends on whether the sensor can operate into an inductive load.

 

[Ian H]

I want to walk in the door, the sensor detects me and turns on the fan.

 

[Ian H]

Other wise could I swap this for a 3 way switch and use that for the fan?

If I can get the wire to it.

 

[bernardgreen]

Then as per the second part of my answer.

In theory you should have a means to isolate the supply to the sensor and fan combination.

Does the fan require an Earth,

 

[EFLImpudence]

A sensor is not a good way to operate the from a behavioural point of view - quick pee in middle of night and other times you might not want it to come on when you are in the room.

 

[Ian H]

But then in summer we don’t have the light on.

Would it work on the switch if I swapped the 2 for a 3? I believe I can have an isolator in the loft.

 

[SimonH2]

Dad used PIRs for the fans at their last house - worked well enough. In the bathroom it was the only way really since there were 3 separate lights so triggering from light wasn't practical. He did put a pull cord hidden in the airing cupboard so it could be turned off - and it wasn't so noisy as to be a problem at night.

 

[EFLImpudence]

Yes, a 3 gang switch would be fine.

An isolator is not, strictly speaking, required but is a good idea and can be placed near the fan.

 

[SimonH2]

That looks like a switched fused connection unit - it would be impractical to swap it unless you want to change the backbox to a double so you can have a three-gang grid with a fuseholder and two switches.

EDIT: Oops, now I look closer I see it is two switches

 

[mattylad]

If you mean that the sensor triggers a timer in the fan then the answer is almost certainly NO

If you mean the timer in the sensor controls how long the fan runs after movement stops then it might work. It depends on whether the sensor can operate into an inductive load.

Bernard, would you mind explaining to me why the answer is NO?
What is the technical reason for it not working? or is there a regulatory reason?

Surely if the sensor output was set to say 10 seconds, then it would drop out 10 seconds after sensing someone, then the fan timer just does it's stuff and turns off?

 

[SimonH2]

A lot would depend on the specific of the sensor and the fan. If the sensor is solid state, and the fan sensitive, then it's possible there could be enough leakage through the sensor to trigger the fan continuously. If the sensor uses a relay for load switching, then without a lamp to provide load, there might be enough capacitive coupling to trigger the fan.
Or it might "just work fine"
It might be that you have to try it and see ...

 

[bernardgreen]

Most if not all Trigger inputs to fan timers are high impedance and can trigger if there is stray capacitively coupled Live on the cable to the trigger input. Normally there is a lamp between trigger input ( switched Live ) and Neutral which absorbs the capacitively coupled energy thus removing the Live, hence the timer is not triggered.

The output from the sensor may not have any internal load to absorb the capacitively coupled energy.

Simon beat me to it

 

[flameport]

Could I use one of these to trigger it when someone goes into the bathroom?
https://www.astra247.com/mini_pir_s...D2Ch3RbHhIBsprPgM1d_mvlNTOsLesqhoCg9MQAvD_BwE

That will be a world of problems, as the control unit won't fit through the hole in the ceiling and it's maximum load is suspiciously small.

Get one of these:
https://www.screwfix.com/p/lap-standalone-pir-360/9695v
which contains a relay for the switched output, and an extractor fan without a timer.

 

[Ian H]

Ok, thanks for the advice so far.

I’m thinking to get rid of the PIR idea and stick to a switch.

The bathroom wall is made of 4x2 and between the double light switch and ceiling will be a couple of noggins that would make it hard to get any wire through. That leaves us with a pull switch and my missus would be happy with a chrome one.

It could possibly go outside the bathroom here:

Inside the bathroom (if it’s allowed) here:

And the loft is converted but I can get above it here (green boards are in the bathroom, pink are in the hall):

Where is the best place?