Dimmer switch fan control

[jkogel]

The home owner has wired his bath exhaust fan with a lighting dimmer switch, the kind that is push-on, push-off and you can vary the current to a bulb. Besides being bad for the fan motor (or is it?), is there any danger to the homeowner? I'm thinking the switch could overheat?

John Kogel
www.allsafehome.ca

[Marc Benz]

Originally Posted by jkogel

The home owner has wired his bath exhaust fan with a lighting dimmer switch, the kind that is push-on, push-off and you can vary the current to a bulb. Besides being bad for the fan motor (or is it?), is there any danger to the homeowner? I'm thinking the switch could overheat?

Using a dimmer switch to run the fan motor is not a good idea it will destory the motor and can ruin the dimmer switch.

However if that is a motor speed control it may be ok depending on what namebrand the exhaust fan is and typically with motor rated speed controller it will slow down the fan motor a bit but when you slow down the fan you will really loose the performace pretty fast.

Merci,Marc

[jkogel]

Pretty sure it's a light dimmer by the appearance of the knob and the on-off feature. Now I'm wondering if it can cause a fire by the motor drawing more current than the switch can handle.

[Bob Elliott]

The motor needs to be on its own switch, in my opinion.

I do not think it can cause a fire , but the motor may burn out.

[Frank P. Newman]

Originally Posted by relliott

The motor needs to be on its own switch, in my opinion. I do not think it can cause a fire , but the motor may burn out.

Given that the power required by a fan is related to the cube of the speed (I think I am remembering that correctly), slowing the motor will reduce the motor current considerably. If that is the case the motor will probably survive ok. I would be more concerned as to whether the current rating of the dimmer is adequate for the full speedload.

All that aside, why would anyone need a variable speed bathroom exhaust fan?