SIRIUS S3 power contactor — 3RT1044-3AH00
The Siemens 3RT1044-3AH00 is a SIRIUS S3 power contactor rated for motor switching at 37 kW on 500 V AC-3 duty, and 55 A on AC-4 at 400 V — that's the heavy reversing or inching load curve, not just steady running. Screw-type terminals on the main circuit accept 2x (10... 50 mm²) stranded or 2x (0.25... 2.5 mm²) solid, so it lands comfortably on motor feeds up to that cross-section.
The AC-3 rating at 500 V — 37 kW — is the number that decides whether this contactor handles your motor. AC-4 at 400 V, 55 A, covers reversing and inching where the contacts open under full load current — a harder duty that drives contact life. The mechanical life is listed at 10,000,000 operations typical, but the electrical life depends on which duty cycle you run: at AC-3 it's rated for 1,000 switching cycles per hour, at AC-4 it drops to 300 per hour. That's the real constraint for a high-cycle application like a conveyor reverser.
Snaps onto 35 mm or 75 mm DIN rail; screw-fastening optional. S3 frame size is 146 mm high, 70 mm wide, 139 mm deep. IP20 on the front with cover; terminal area is IP00.