Zone dampers are used with a zone control system to direct the flow of air in the HVAC central system duct work. A two-wire zone damper is designed to power the damper blade closed and spring return it open. When a zone thermostat calls for heating or cooling, its zone damper spring returns open to provide heated or cooled air to the zone. When the zone thermostat is satisfied, the damper is powered closed preventing conditioned air from entering the zone.
A two-wire zone damper incorporates a 24 volt motorized actuator that powers the damper blade closed. The motor is impedance protected which allows it to stall at the end of the damper travel without having to have an end switch to disrupt the power. When power is removed, the spring return mechanism drives the damper blade to the open position.
A three-wire zone damper requires a motorized actuator that powers the damper blade in both directions. Three-wire zone damper actuators typically have heavier torque ratings which allow them to be used on larger size dampers.