Image is Representational - See Manufacturer Specs | Timer Fan and Light Switch - Black - 120VAC. Voltage is applied to the unit at all times via the black and white wires. When the switch is placed in the ON position power is applied to the lamp and fan output. When the switch is placed in the TIMED position the power is removed from the lamp output and the fan output stays on for the preset delay time. After the delay time the power is removed from the fan output.