What is the difference between fail-safe and non-fail-safe actuators?

Fail-safe actuators are designed to drive to a predetermined safe position (fully open or fully closed) when power is lost, using either a mechanical spring (spring-return), capacitive energy storage (Belimo SuperCap), or battery backup to provide the motive force. Non-fail-safe actuators simply stop in their last position on power loss (fail-in-place) and are used in applications where the failure position does not create a safety hazard — such as VAV cooling-only boxes or non-critical exhaust dampers. The fail-safe requirement is driven by code: smoke control dampers (UL 555S), stairwell pressurization, elevator hoistway vents, and freeze protection valves all require fail-safe operation per the IBC or IMC. The selection impacts first cost (fail-safe actuators cost 30–50% more), wiring (spring-return actuators require separate power for the spring mechanism), and energy efficiency (spring-return actuators draw holding current continuously, though modern designs have reduced this to 0.5–1W).