I have a humidity sensing exhaust fan in my bathroom. When the fan has power and senses humidity, it will run the fan until the humidity is removed. If you want to turn the fan on manually (in a stinky situation) you can switch the power off momentarily and then back on and it will run for a pre determined amount of time.

In order to make the fan dummy-proof and to prevent mold from growing, I do not want to give users the ability to turn off power to the fan. I could just eliminate the switch and the humidity sensor would take care of the rest, but then the user would not have the ability to momentarily cycle the power to run the fan manually when there is stink but no humidity.

So what I need is a switch that always springs back to the on position. I have found this type of switch in different physical styles that won't neatly work with a wall plate. I need it to be a typical residential/commercial rocker or toggle switch.

The closest I have come to such a thing is the Leviton 1256 but it's center-off instead of center-on. Is it possible to reverse the function of the switch? Or is there another switch out there that would work better? Or is there another more elegant solution all together that I haven't though of?

 

There are blank wall plates you could easily drill a hole in to mount a button switch with a set of normally closed momentary contacts.
https://www.automationdirect.com/ad...m_pushbuttons_illuminated_-a-_non-illuminated

 

Those common little push button switches need to be rated for the voltage and amperage the fan will draw.

What I gather from your description is that when someone showers you want the fan to come on automatically until dehumidified. And if someone drops a stool you want the dropper to be able to activate the fan for - lets say 15 minutes.

It would seem to me like you simply need a humidity sensor to activate the fan for 15 minutes beyond the low level of humidity sensed. Then you'd just need a simple PB switch to bypass the sensor into thinking there's humidity, and the fan comes on for the preset period of time. I don't think you need more switches than just the one. Unless for some reason you want to be able to turn the sensor off altogether.

 

One like this?

 

There are blank wall plates you could easily drill a hole in to mount a button switch with a set of normally closed momentary contacts.
https://www.automationdirect.com/ad...m_pushbuttons_illuminated_-a-_non-illuminated

Thanks for the replies! I will probably try out the push button idea and drill a hole in a blank wall plate.

 

Ive done this lots of times.
My fans were set to trickle during the day. Then when a PIR sensed a person it kicked into high speed for a pre determined period. That did away with the need for the unreliable hum sensors, but delivered a clear bathroom along with zero background noise at night.
I used a combination of off the shelf ccts along with a DC fan which allowed better speed control & lower energy consumption.