SIRIUS S3 Power Contactor — 24 VDC Coil, Screw Terminals
The Siemens 3RT1044-3BB40-ZX95 is a SIRIUS-branded power contactor in frame size S3, rated for motor switching up to 37 kW at 500 V and 18.6 kW at 690 V. The 24 VDC coil pulls in at 0.8 of rated voltage and drops out below that threshold, with an arcing time of 10 to 15 ms at DC and a DC switching window of 14 to 20 ms. Main circuit connections use screw-type terminals accepting 2x (10 to 50 mm²) stranded or 2x (2.5 to 16 mm²) solid/stranded; control terminals take 2x (0.25 to 2.5 mm²) solid.
What the Ratings Mean for Your Panel
AC-3 switching at 1000 operations per hour is the motor-duty benchmark — this contactor handles frequent starting of squirrel-cage motors at that rate. AC-4 at 55 A and 400 V covers inching and plugging duty, where the contactor makes and breaks stalled-rotor current; the 300 ops/h ceiling reflects the higher thermal stress of that cycle. Pollution degree 3 means the contactor is rated for conductive pollution typical of industrial control panels — no additional conformal coating required for normal environments. The IP20 front enclosure with optional cover/box terminal protects against finger contact; the terminal block itself is IP00, so panel builders must maintain clearance in the wiring compartment.
Mounting and Integration
Mounts via screw fixing or snap-on onto 35 mm or 75 mm standard mounting rail. Side-by-side mounting is permitted, so multiple contactors can pack tightly on the rail without derating for heat buildup. Dimensions are 70 mm wide, 146 mm high, 152 mm deep — fits standard S3 panel cutouts. Operating temperature range is -25 to +60 °C; storage range extends from -55 to +80 °C.