The Siemens 3RW4422-3BC36 is a SIRIUS soft starter rated for 50 A at 40 °C, with an insulation voltage of 690 V and a control supply of 115 V at both 50 and 60 Hz. It uses thyristors for the ramp-up and includes an integrated bypass contact system that switches the motor to line power once at speed, which cuts heat dissipation in the panel and extends the life of the semiconductor stack. The minimum load is 8% of the rated current, meaning it handles lightly loaded conveyors or pumps without dropping out.
The 690 V insulation voltage means it can be used on 400 V or 480 V systems with plenty of headroom, and it meets pollution degree 3 per IEC 60947-4-2, which is the standard for industrial environments with conductive dust or humidity. The inside-delta circuit configuration is supported, which lets you connect the soft starter in the motor delta loop rather than in-line. This reduces the current the unit sees by a factor of √3, effectively giving you a higher motor rating from the same device — useful when the motor FLA exceeds the soft starter's line rating. Wire length to the motor can be up to 500 m without additional output reactors, which covers most plant-floor runs. The main circuit uses box terminals accepting 10 AWG to 1/0 AWG stranded, and the auxiliary/control circuit uses spring-loaded terminals for 24 to 16 AWG — no tools needed for the control wiring.
Mounting is by screw fixing, not DIN rail, so plan for a backplate or sub-panel. Mounting position is flexible: vertical surface, rotatable ±90°, and tiltable ±22.5° front-to-back, which helps when fitting into existing layouts. Clearance requirements: 100 mm above, 75 mm below, and 5 mm at the sides. The 5 mm side clearance is tight — you can pack units close together, but the top and bottom gaps are needed for airflow and cable bending radius. Storage temperature range is -25 to +80 °C, operating ambient up to 60 °C.
No need to hunt for surplus or cross-reference a substitute — the 3RW4422-3BC36 is the current catalog number. The integrated bypass and overload protection mean it replaces older soft starter + contactor + overload combinations in one footprint.