The Active Air ACSC fan speed adjuster was designed especially for centrifugal fans to help prevent damage to fan motors, ensuring longer life. It will correctly adjust the speed of fans without causing the motor to hum. This 120 volt speed adjuster has three settings, allowing you to simply increase or decrease the fan speed, and set a minimum fan idle speed between 0 to 100%. Rated for 15 amps, this speed adjuster features an electronic auto-resetting circuit breaker that has been added in the event of a power surge. The breaker remains tripped for a period of time set by an external timing capacitor and then is automatically reset. For use with permanent split capacitor type motors, all Hydrofarm inline fans, and Active Air booster fans.