SIRIUS S3 Power Contactor — 37 kW at 500 V
The Siemens 3RT1044-1AH28-0PA4 is a SIRIUS size S3 power contactor rated for 37 kW at 500 V in AC-3 duty — that's the motor-switching rating that governs the real-world fit for pumps, fans, and compressors up to that load. The AC-3 maximum switching rate of 1 000 cycles per hour means it can keep up with frequent start-stop sequences on a conveyor or batch process without exceeding thermal limits. Mechanical life is typical at 10 000 000 operations, so the contactor itself outlasts most panel rebuild cycles. The coil operates on 50 Hz or 60 Hz supply with a rated voltage of 48 V, and the operating range spans 0.8 to 1.1 times nominal at 50 Hz and 0.85 to 1.1 at 60 Hz — wide enough to handle a sagging line without dropping out. The 24 V DC auxiliary contact rating is 10 A, which covers pilot-duty loads like PLC inputs or indicator lamps.
Mounting and Wiring — DIN Rail, Screw Terminals
Dimensions are 146 mm high, 80 mm wide, 139 mm deep. Main circuit terminals are screw-type, accepting solid conductors from 2x 0.5 mm² up to 2x 4 mm², and stranded from 2x 10 mm² up to 2x 50 mm². That range covers control wiring through motor feeders. Terminal protection is IP00, but the front face carries IP20 with the cover or box terminal fitted — enough for finger-safe touch protection inside a closed panel.
Environmental and Duty Ratings
Switching rates vary by duty class: AC-1 (resistive) max 1 000 cycles/h, AC-2 (slip-ring motors) max 400 cycles/h, AC-3 (squirrel-cage motors) max 1 000 cycles/h, AC-4 (plugging/inching) max 300 cycles/h.