The Siemens SIRIUS 3RT1044-3AL20-ZW97 is a size S3 power contactor rated for motor switching at 37 kW on a 500 V line and 18.6 kW at 690 V under AC-3 duty — the standard category for squirrel-cage motors during starting and running. That 690 V rating makes it a natural fit for 690 V industrial networks common in mining, pumping, and conveyor applications where the line voltage steps above the 400 V tier. The contactor carries a pollution degree 3 rating, meaning it's designed for the conductive-dust and humidity environment inside a typical industrial enclosure, not a clean-room panel.
The screw-type terminals on the main circuit accept solid wire from 0.25 to 2.5 mm² (two conductors) and stranded from 10 to 50 mm² (two conductors), so it handles both control-circuit pigtails and power conductors without a separate lug kit.
Key ratings for the buyer's decision
The AC-3 motor power ratings (37 kW at 500 V, 18.6 kW at 690 V) are the ones that govern motor selection — not the thermal current. The contactor also carries AC-1 resistive ratings (not listed here) but the AC-3 number is what an engineer checks first. Mechanical life is typical at 10 million operations, so it's not a wear-item on a normal maintenance schedule.