The 3RK4320-3PQ51-1BA3 is a SIRIUS reversing starter — meaning it handles forward/reverse motor direction in a single enclosure, saving panel space over two separate contactors. The 12 A rating at 400 V AC-3 (motor duty) tells you it switches induction motors up to that current under full load, not just resistive loads. The Class 10 trip curve means it disconnects within 10 seconds at 600% overload — right-sized for standard squirrel-cage motors that don't need the longer delay of Class 20. It communicates over AS-Interface (the protocol is supported), with 2 digital inputs onboard for local sensors or pushbuttons. The control supply is 24 V DC (20.4...26.4 V range), so it drops into a standard 24 V control panel without a separate supply module.
The enclosure measures 245 mm wide x 215 mm high x 205 mm deep — that's a compact footprint for a reversing starter with integrated brake control. It mounts on a vertical surface with +/-180° rotation possible, and can be tilted forward/backward by +/-22.5° on that surface, giving flexibility in tight cabinets. IP54 protection means it's dust-protected and splash-resistant — suitable for dry indoor industrial environments but not for washdown zones.
Motor protection and brake control in one unit
The motor protection uses a bimetal overload relay — a proven thermal model that tracks motor heating directly. Short-circuit protection is handled by upstream circuit breakers (not fuses), which simplifies coordination and reset. The unit includes a motor brake output for 400 V AC, so it can control a mechanical brake on the motor shaft without an external contactor. Rated for 80 operating cycles per hour minimum — that's one start every 45 seconds, which covers most conveyor and pump cycling. For higher-demand applications, the SN 31920 duty ratings are 50% (low demand rate) and 75% (high demand rate), meaning it's designed for continuous rated current at those duty cycles.