SIRIUS S3 Power Contactor for Motor Loads
The Siemens 3RT1044-1XB40-0LA2 is a SIRIUS-brand power contactor in the S3 frame size, designed for switching three-phase induction motors in control panels. Its AC-3 rating of 37 kW at 500 V and 18.6 kW at 690 V defines the motor load it can handle under typical starting and running conditions — the rating that governs real-world sizing, not the higher AC-1 resistive figure. The 24 VDC coil with a pick-up threshold of 0.7x rated value (about 16.8 V) and dropout below that ensures reliable pull-in even on a sagging control supply.
Panel Integration and Mounting
Mounts via screw and snap-on onto 35 mm or 75 mm standard DIN rail — the dual-rail option is useful when the contactor sits in a high-density panel where 75 mm rail provides better mechanical support for the S3 frame. Side-by-side mounting is permitted, so multiple contactors can be ganged without spacing blocks. Clearance requirements: 10 mm upwards, 10 mm downwards, 10 mm at the side, and 20 mm forwards. The envelope is 176 mm high by 70 mm wide by 152 mm deep.
Termination and Wiring
Main circuit terminals are screw-type, accepting a wide range of conductor sizes: solid or stranded 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), and up to 2x (0.75 to 4 mm²) for control wiring. The main power terminals accept 2x (10 to 50 mm²) stranded, with a maximum of 35 mm² for AC-1 rated connections. This range covers most panel wiring from control-circuit signal wires up to motor feeder cables.