ECN Forum Forums General Topics of the Trade General Discussion Area Exhaust Fan Speed Control

If I had a 3-phase RTU exhaust fan controlled by a 120V contactor coil, what are my options as far as speed control of the motor?

What if the control circuit operated at 24 volts?

And finally, does a motor need to be rated for variable speed for a low, medium, and high speed controlling device?

Thanks in advance.