This controller senses when a clothes dryer is drawing 1.2 AMP of current. When this occurs a relay contact closes turning the dryer vent booster fan ON. When current drops below the 2 AMP threshold the relay contacts open turning the booster fan OFF. The sensor is designed to mount in a standard electrical box. The AMP Sensor may be placed in an electrical box adjacent to the junction box in which the wires supplying power to the dryer are located (see back of this page). The dryer supply neutral (white) wire passes through the center of the AMP Sensor donut. No physical connection is made.