The Siemens SIRIUS 3RT1045-1AK68-0PA4 is a size S3 power contactor rated for motor switching up to 45 kW at 500 V in AC-3 duty, with a mechanical life of 10 million cycles typical.
The AC-3 rating of 45 kW at 500 V is the key selection figure for motor starting — it tells you this contactor can handle the inrush and break the running current of a standard squirrel-cage induction motor up to that power. At 690 V the same duty drops to 21.1 kW, which is the derating you need to account for when the line voltage is higher. The AC-1 resistive rating isn't listed as a single current, but the maximum operating rate of 900 operations per hour under AC-1 gives a sense of its thermal cycling capability for heater or lighting loads. For the control circuit, the contactor's coil draw at 24 V is 10 A — that's the inrush, not the hold, so size your PLC output or interposing relay for that peak. At 230 V the coil draw drops to 6 A, and at 400 V it's 3 A. The arcing time across the main poles runs 10 to 25 ms at AC, with a narrower window of 10 to 15 ms typical, which matters for coordinating upstream fuse or breaker clearing curves.
Mounting and Wiring Integration
Dimensions are 70 mm wide, 146 mm high, 188 mm deep — the S3 frame fits a standard DIN-rail envelope. Side-by-side mounting is permitted with no derating gap, so you can pack several contactors on a rail for multi-motor groups. The main circuit accepts solid conductors up to 2x (0.5 to 1.5 mm²) and 2x (0.75 to 2.5 mm²), with a maximum of 2x (0.75 to 4 mm²) for the smaller terminals; stranded goes up to 2x (10 to 50 mm²) on the power side. Front IP20 with a cover or box terminal keeps fingers out; the terminal body itself is IP00, so the panel enclosure provides the overall ingress protection.