SIRIUS S3 power contactor — 55 A AC-4, 37 kW at 500 V
The Siemens 3RT1044-3BB44-3MA0 is a SIRIUS S3-frame power contactor, rated for 55 A in AC-4 duty at 400 V — that's the switching category for reversing, inching, and plugging motor loads where the contactor makes and breaks stalled-rotor current. At 500 V it carries 37 kW, sized for a typical 37 kW four-pole induction motor on a 500 V three-phase line. Mounts on 35 mm or 75 mm standard DIN rail via screw and snap-on fastening; side-by-side mounting is permitted. S3 frame: 146 mm high, 70 mm wide, 201 mm deep. Main current circuit terminations are screw-type, accepting 2x (10–50 mm²) stranded or 2x (0.25–2.5 mm²) solid conductors. The front of the contactor carries IP20 protection with the cover or box terminal fitted; the terminal itself is IP00, so panel builders should account for that in the enclosure IP rating.
DC switching capacity — what the curve means
The DC switching ratings are given at several voltage points: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V, 6 A at 230 V, and 3 A at 400 V. These are the maximum resistive DC currents the contactor can break at each voltage — not a continuous carry rating. For a 24 VDC control circuit or a small DC motor brake, the 10 A figure gives headroom; above 60 V the curve drops steeply, so a 110 VDC solenoid bank pulling 1 A is at the limit.
Panel integration notes
Screw and snap-on onto 35 mm or 75 mm rail. Side-by-side mounting is allowed. Depth is 201 mm.