The Siemens SIRIUS 3RW4037-2BB15 is a soft starter in the S2 frame size, rated 63 A at 40 °C with a 110-230 V DC control supply. It includes an integrated bypass contact system that removes the thyristors from the circuit once the motor is at full speed, reducing heat dissipation and extending the life of the power electronics. The unit mounts via screw or snap-on to a DIN rail, fitting a standard panel enclosure.
The integrated bypass contact system means the thyristors only handle the start and stop ramps; during run, the bypass relay carries the full load current, so the soft starter runs cooler and the thyristors see less thermal cycling. This is standard on SIRIUS 3RW40 series and avoids the need for an external bypass contactor.
The 3RW4037-2BB15 measures 55 mm wide, 160 mm high, and 170 mm deep — a compact S2 footprint that fits a standard 55 mm DIN-rail slot. Screw and snap-on mounting lets the panel builder clip it onto the rail or bolt it to a backplate. Clearance requirements: 60 mm above, 40 mm below, and 30 mm to the side for airflow and wiring access. Main power terminals accept screw-type connections: solid wire 2x (0.25-2.5 mm²) and stranded 2x (1.5-25 mm²). Auxiliary and control circuits use spring-loaded terminals, which speed up wiring and resist vibration loosening. The control supply is 110-230 V DC, so a separate DC power supply is needed — no direct AC tap.