The Siemens 3RT1045-3AF06 is a SIRIUS S3 power contactor, rated for switching motor loads up to 37 kW at 400 V in AC-3 duty — the standard category for squirrel-cage motors during starting and running. That 37 kW figure at 400 V is the one that governs motor fit; the part also carries a 45 kW rating at 500 V and 21.1 kW at 690 V, so it scales with line voltage. Screw-type terminals on the main circuit accept solid conductors from 0.25 to 2.5 mm² (two per clamp) and stranded from 10 to 50 mm² — wide enough for the motor leads this size contactor typically handles.
The AC-4 rating of 66 A at 400 V covers plugging and inching duty, where the motor is reversed or jogged under full load; that's a higher current because the contacts must handle locked-rotor conditions repeatedly. Mechanical life is typical at 10,000,000 operations, and the maximum switching frequency ranges from 300 cycles/hour in AC-4 up to 1,000 cycles/hour in AC-3. For a conveyor or pump running a few starts per hour, the AC-3 rate is generous; for a high-cycle indexing table, check the AC-4 limit. Coil operating range is 0.8 to 1.1 times the rated voltage at 50 Hz, with an arcing time of 10 to 15 ms and a total closing time of 10 to 25 ms. That's typical for a contactor this size — fast enough for most motor starts, but not for precision timing circuits.