The Siemens 3RW4423-1BC35 is a SIRIUS soft starter, a thyristor-based motor controller that reduces inrush current during start-up and provides a controlled ramp-down for pumps, conveyors, and fans. It is rated for a motor current of 62 A at 40 °C, derating to 55 A at 50 °C and 50 A at 60 °C, so the ambient temperature in the enclosure directly governs the maximum motor you can hang on it. The control supply is 115 V at both 50 and 60 Hz, which matches standard North American control voltages.
The integrated bypass contact system means that once the motor is up to speed, the thyristors are shorted out, eliminating heat dissipation in the soft starter during run — a critical factor for panel thermal management. The adjustable current limitation lets you set the start current between the minimum load of 8% and the full rated current, which is useful for soft-starting lightly loaded machines without oversizing the starter.
Mounting is by screw fixing on a vertical surface, with the unit rotatable ±90° and tiltable ±22.5° forward and back, giving flexibility in panel layout. Clearance requirements: 100 mm above, 75 mm below, 5 mm at the sides. The main circuit uses box terminals accepting 2x (4... 50 mm²) stranded or 2x (10... 1/0) AWG using both clamping points. The auxiliary and control circuit uses screw-type terminals for 2x (0.5... 2.5 mm²) solid. Maximum motor cable length is 500 m — long enough for most industrial runs but worth checking for distributed motor installations.