SIRIUS Power Contactor, Size S3 — 3RT1045-3BD40
The Siemens 3RT1045-3BD40 is a SIRIUS power contactor in Size S3, rated for 45 kW at 500 V in AC-3 duty — the standard motor-switching category per IEC 60947-4-1. That 45 kW figure at 500 V is the load it can switch under full motor starting conditions; at 690 V the same contactor carries 21.1 kW. AC-3 switching means it makes and breaks a motor load at full locked-rotor current, so the 45 kW rating governs the motor nameplate it can handle. Mounting is screw-and-snap-on onto 35 mm or 75 mm standard mounting rail — the 75 mm option is unusual for a Size S3 frame and gives panel builders flexibility when rail spacing is non-standard.
Switching Performance and Mechanical Life
Electrical life depends on duty: at AC-3 (motor start/run) the maximum switching rate is 1 000 operations per hour; at AC-4 (plugging, inching, reversing) it drops to 300 operations per hour.
Environmental Range and Terminal Capacity
Solid wire connections accept 2x (0.25 to 2.5 mm²) for control circuits; stranded main conductors take 2x (10 to 50 mm²). The auxiliary contact block (if fitted) shares the same coil suppression — verify free-wheel diode polarity before energising inductive loads downstream.