The Siemens 3RW4422-1BC36 is a SIRIUS-brand soft starter, built for three-phase induction motors where you need to dial back the inrush and mechanical shock of a direct-on-line start. It uses thyristors to ramp the voltage up, then an integrated bypass contact system takes over once the motor is at speed, so the thyristors aren't sitting there heating up the panel all shift long. That bypass is a real plus out here in the grease — less heat means less trouble for the gear next to it. Rated at 50 A at 40 °C, it handles a 3-phase motor up to that current, derating to 45 A at 50 °C and 40 A at 60 °C. Operating frequency is 50 to 60 Hz, and it's designed for a pollution degree of 3 per IEC 60947-4-2 — meaning it's comfortable in the typical dusty, conductive environment of a motor control center.
Mounts with screw fixing — not a snap-on DIN rail job, so plan for that in the panel layout. The dimensions are 192 mm high, 170 mm wide, and 270 mm deep. That depth is worth noting if you're squeezing it into a shallow enclosure. Clearance needs: 100 mm above, 75 mm below, and just 5 mm at the sides. The mounting position is flexible — vertical surface, rotatable ±90°, tiltable ±22.5° front-to-back — so you can fit it to the available real estate. Main circuit connections use box terminals, accepting stranded wire from 4 to 50 mm² (2x conductors). The maximum wire length to the motor is 500 m — keep that in mind if you're running a long feeder from the MCC to a remote pump.
Protection and adjustments
Built-in motor overload protection is standard, so you don't always need a separate overload relay. There's also intrinsic device protection for the soft starter itself. The current limitation is adjustable — you can set the start current from a minimum load of 8% up to whatever the motor needs. An external reset input is there, handy for remote reset from a control room. If there's a fault, the display shows a fault signal, which beats chasing a blinking LED. Supports inside-delta circuit wiring — that's a configuration where you wire the soft starter inside the motor's delta connection, reducing the current the starter sees. Useful for bigger motors where you want to use a smaller frame size.