The Siemens 3RT1045-1BB44 is a SIRIUS power contactor in frame size S3, rated for motor switching up to 45 kW at 500 V and 21.1 kW at 690 V. The 24 VDC coil pulls in at 0.8x rated voltage and drops out at 1.1x, with a pick-up delay of 14 to 20 ms and arcing time of 10 to 15 ms — numbers that matter when coordinating control logic timing in a safety circuit or sequence interlock. Screw-type terminals on the main circuit accept solid conductors up to 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²), and stranded up to 2x (10 to 50 mm²). The control circuit terminals handle 2x (2.5 to 16 mm²) solid or stranded.
Side-by-side mounting is permitted. Dimensions are 70 mm wide, 146 mm tall, 201 mm deep — the depth is the dimension that often catches panel layouts designed around smaller frames. Verify the 201 mm projection from the rail before committing the backplate layout.
Switching Capacity and Duty Ratings
The AC-3 rating of 1000 operations per hour at full motor current sets the thermal limit for frequent starting — a conveyor or pump cycling every 3.6 seconds would hit this ceiling. AC-4 (inching/plugging) drops to 300 ops/h, reflecting the higher arc energy during reversal. For resistive loads (AC-1), the contactor handles 900 ops/h. DC switching capacity is limited: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V — the arc extinction in DC is harder, so these are the practical break limits. At 400 V, the AC-2 rating (slip-ring motor duty) is 37 kW, and AC-4 (reversing) is 66 A. The 690 V rating of 21.1 kW is the same contactor, same coil — no voltage-tap change needed.