The Siemens 3RT1044-3KB44-0LA0 is a SIRIUS S3-frame power contactor rated for motor switching in the 55 A AC-4 class at 400 V, delivering 37 kW at 500 V and 18.6 kW at 690 V. That AC-4 rating means it's built for reversing, plugging, and inching duty — the hardest start-stop cycles a contactor sees, where the motor is re-energized while still spinning or under load. The coil pulls 24 V DC with a 10 A inrush at that voltage, and the contactor closes in 14–20 ms with an arcing time of 10–15 ms. For lighter motor starting (AC-2), it handles 30 kW at 400 V. The screw-type terminals on the main circuit accept 2x (10–50 mm²) stranded and 2x (0.25–2.5 mm²) solid; auxiliary terminals take 2x (2.5–16 mm²) solid or stranded.
Duty cycles and endurance
Maximum mechanical endurance is 10 million operations. Switching frequency varies by duty: 1 000 cycles/hour for AC-1 and AC-3, 400/h for AC-2, and 300/h for AC-4. The AC-4 limit is the binding constraint for severe applications — at 300 cycles/hour, the contactor is thermally limited by the arc energy during reversal or inching.