The Siemens SIRIUS 3RW4424-3BC44 is a soft starter designed to ramp induction motors up to speed, reducing inrush current and mechanical shock. It is rated 81 A at 40 °C (73 A at 50 °C, 64 A at 60 °C) on a 230 V supply at 50/60 Hz, with an insulation voltage of 690 V. Built with thyristors and an integrated bypass contact system, it handles continuous motor current through the bypass once the motor is up to speed, reducing heat dissipation in the soft starter. Adjustable current limitation lets you set the starting current between 8% and 100% of the motor FLA.
Above 40 °C, you must derate: 73 A at 50 °C, 64 A at 60 °C. If your panel ambient runs at 50 °C, size the motor load to 73 A or less. Minimum load is 8% of the rated current — so at 81 A, the soft starter will reliably control a motor drawing as little as 6.5 A. Below that, the thyristor firing angle may not be consistent. Motor overload protection is built in, and intrinsic device protection (over-temperature, phase imbalance) is standard. An external reset input allows remote fault clearing. The inside-delta circuit connection option is available — this reduces the soft starter current rating requirement to 58% of the motor FLA when wired in delta, useful for larger motors where the soft starter frame size would otherwise be larger.
Dimensions: 192 mm high, 170 mm wide, 270 mm deep. Mounting is screw fixing on a vertical surface, rotatable ±90° and tiltable ±22.5° front-to-back. Clearance requirements: 100 mm above, 75 mm below, 5 mm at the sides for airflow. Main current circuit uses box terminals accepting stranded 2x (4... 50 mm²). Auxiliary and control circuits use spring-loaded terminals for 2x (0.25... 1.5 mm²) solid. Maximum motor cable length is 500 m. Storage temperature range is -25 to +80 °C; operation is rated to 60 °C ambient. The unit has a display for fault signals.