Integrator's Quick Assessment
The Siemens 3RT1045-1AK20 is a SIRIUS S3-frame power contactor rated for motor switching at 45 kW on a 500 V AC-3 supply and 21.1 kW at 690 V AC-3. Front protection is IP20 with the cover or box terminal installed; the terminal body itself is IP00, meaning the wiring compartment must be inside a rated enclosure. Operating ambient spans -25 to +60 °C, with storage from -55 to +80 °C — adequate for most indoor industrial panels but verify if the panel ambient exceeds 60 °C near ovens or furnaces.
Motor Duty and Switching Performance
This contactor is sized for AC-3 motor starting and AC-4 inching/plugging duty. At AC-3 it manages up to 1 000 switching cycles per hour; at AC-4 the rate drops to 300 cycles per hour due to the higher electrical stress of breaking locked-rotor current. The mechanical life is typical at 10 000 000 operations, so the limiting factor in high-duty-cycle applications will be electrical wear on the contacts, not the mechanism. Coil operating range spans 0.8 to 1.1 times rated voltage at 50 Hz and 0.85 to 1.1 at 60 Hz, with an arcing time of 10 to 15 ms and total opening time of 10 to 25 ms at AC. For a 24 VDC control circuit, the auxiliary contact ratings are 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V — sufficient for pilot duty on most PLC outputs but check the inrush of the connected load.
Wiring and Panel Integration
Main power terminals accept solid conductors: 2x (0.5... 1.5 mm²), 2x (0.75... 2.5 mm²), or max 2x (0.75... 4 mm²). Stranded connections use 2x (10... 50 mm²) for the main circuit. The auxiliary and coil terminals accept 2x (2.5... 16 mm²) solid or stranded.