The Siemens 3RT1044-1BW40 is a SIRIUS power contactor in size S3, designed for switching motor loads and resistive loads in industrial control panels. It mounts via screw or snap-on onto 35 mm or 75 mm standard DIN rail, with side-by-side mounting permitted for multi-contactor groups. Rated for 37 kW at 500 V in AC-3 duty (motor starting/switching) and 55 A at 400 V in AC-4 duty (reversing/inching), the contactor handles the mechanical endurance of 10 million typical cycles. The AC-3 switching rate reaches 1000 operations per hour; AC-4 is derated to 300 operations per hour. Main circuit connections use screw-type terminals. Solid wire acceptance ranges from 2x 0.5...1.5 mm² up to 2x 0.75...4 mm²; stranded wire accepts 2x 10...50 mm². The auxiliary/control circuit accepts 2x 2.5...16 mm² solid or stranded. The enclosure carries IP20 on the front with the cover or box terminal fitted; the terminal itself is rated IP00. Pollution degree 3 applies, meaning the contactor is suitable for industrial environments with conductive pollution.
Mounting and Panel Integration
Dimensions are 146 mm high, 70 mm wide, 152 mm deep. The 70 mm width is a standard S3 footprint, allowing direct replacement in panels where a size S3 contactor was originally specified. Snap-on mounting onto 35 mm or 75 mm DIN rail speeds installation; screw mounting is also supported for vibration-prone environments. Side-by-side mounting is explicitly permitted, so multiple contactors can be ganged without additional spacing — useful for grouped motor starter assemblies where panel width is constrained.
Lifecycle and Sourcing
Compliance documentation includes RoHS compliance with a substance prohibition date of 05/01/2012. The contactor carries no known material compliance gaps for EU or global industrial markets.
Ratings in Context
The 37 kW rating at 500 V AC-3 is the headline motor-switching capacity. At 690 V, the motor power rating is 18.6 kW, reflecting the reduced current capability at higher voltage. For resistive loads (AC-1), the switching rate is 1000 operations per hour; for AC-4 reversing duty, the rate drops to 300 operations per hour due to increased contact wear. The DC switching ratings are modest: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V. Arcing time in DC circuits is 14...20 ms, compared to 10...15 ms for AC. This contactor is primarily intended for AC motor loads; DC applications should be verified against the load break current. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The wider storage range reflects handling and transport conditions, not running operation.