The Siemens SIRIUS 3RW4423-1BC46 is a soft starter designed to ramp AC induction motors up to speed, reducing inrush current and mechanical stress during start-up. It switches the motor phases via thyristors and includes an integrated bypass contact system that, once the motor is at full speed, shorts out the thyristors to eliminate heat dissipation and extend service life. The unit carries a rated operational current of 62 A at 40 °C, derating to 55 A at 50 °C and 50 A at 60 °C, and is rated for a supply voltage of 230 V at both 50 and 60 Hz.
If the ambient inside the enclosure runs to 50 °C, the available current drops to 55 A; at 60 °C, it is 50 A. That derating starts at 40 °C, so any installation above that temperature must be factored into the motor full-load current.
The unit measures 192 mm high, 170 mm wide, and 270 mm deep, and uses screw fixing for mounting. Clearance requirements are 100 mm above, 75 mm below, and 5 mm at the sides for airflow and cable access. The main current circuit uses box terminals accepting stranded wire from 4 to 50 mm² (or 10 to 1/0 AWG using both clamping points).
Protection and Control Features
Built-in motor overload protection and intrinsic device protection are standard. The adjustable current limitation lets you set the start current between 8% and 100% of the rated current, which is useful for soft-starting pumps or conveyors that need a gentle ramp. An external reset input and a fault display are provided. The unit supports inside-delta circuit wiring, which allows a smaller frame size for a given motor current by connecting the soft starter in the delta legs rather than the line.