The Siemens SIRIUS 3RT1045-1AH20 is an S3-frame power contactor rated for motor switching at 45 kW on a 500 V 50 Hz line and 21.1 kW at 690 V. That 500 V rating tells you it's sized for a 3-phase motor pulling around 65 A in AC-3 duty — common for medium conveyors, pumps, or compressors in a 400 V to 500 V plant. The 690 V rating covers the 575/600 V class used in North American heavy industrial lines.
The AC-3 switching rate of 1 000 operations per hour is the motor-duty limit — that's about one start every 3.6 seconds, which covers most conveyor and pump cycling. AC-4 drops to 300 per hour, reflecting the higher wear from plugging or inching. If your application needs frequent reversing, that 300/h ceiling is the one to watch. In a normal motor-starting cycle you'll get fewer electrical operations before the contacts wear, but the mechanical figure tells you the solenoid and linkage are built for the long haul. IP20 on the front with the cover or box terminal installed — that's finger-safe for the operator side. The terminal itself is IP00, so the wiring compartment needs enclosure protection in a washdown or outdoor cabinet.
That 50 mm² stranded capacity is generous for an S3 contactor — it lets you land a 2/0 AWG equivalent without a ferrule or pin adapter. The auxiliary contacts handle 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V, which covers most PLC output and relay coil circuits.