Intermatic FD34H 4-hour spring wound timer switch, ivory

Intermatic FD34H spring wound timer

The Intermatic FD34H is a wire-in wall switch timer that uses a mechanical spring wound mechanism to control electrical circuits. It provides up to four hours of timed operation without requiring external power for the timing function. This SPDT device suits installers who need a simple, reliable time control for lighting or ventilation loads.

4-hour maximum timing range

The single specification that determines suitability is the four hour maximum timing interval set by the spring wound mechanism. The timer cannot be programmed for periods longer than this limit, so applications requiring overnight or multi-day schedules need a different solution. The SPDT contact arrangement allows switching between two separate circuits during the timed period.

Mechanical operation under sustained load

Because the timer relies on a wound spring rather than an electronic oscillator, its timing accuracy remains consistent regardless of how long the connected load draws current. There is no thermal drift or battery depletion to alter the countdown during continuous operation. The mechanism resets automatically after each cycle, ready for the next manual wind.