The Siemens SIRIUS 3RW4436-6BC44 is a soft starter rated 281 A at 40 °C, 230 V, 50/60 Hz, with adjustable current limitation and integrated motor overload protection. It supports inside-delta circuit wiring, which reduces the current through the thyristors and allows a smaller unit for the same motor current — a common choice for larger motor starts where panel space is tight.
The insulation voltage is rated 690 V. The operating frequency covers 50 to 60 Hz, making it suitable for both IEC and NEMA line frequencies. The adjustable current limitation lets you set the starting current between the minimum load of 8 % and the full rated current — useful for limiting inrush on weak supplies or protecting driven equipment. The inside-delta circuit means the thyristors sit in the delta legs of a six-wire motor, so the unit can be smaller for a given motor rating; confirm the motor has six accessible leads before specifying this wiring.
Dimensions: 170 mm wide, 200 mm high, 270 mm deep. The 270 mm depth is notable: it needs a deep enclosure or a back-to-back gland plate clearance. Clearances: 100 mm upwards, 75 mm downwards, 5 mm at the side for airflow and wiring. The main current circuit uses busbar connection; stranded cable from 25 to 120 mm² or fine-stranded 16 to 95 mm² for the power terminals. Auxiliary contacts accept solid 2x (0.5 to 2.5 mm²) or stranded 2x (20 to 14 AWG). The maximum wire length to the motor is 500 m — watch for voltage drop and reflected-wave effects on long cable runs, especially with the thyristor switching.
Fault signaling and protection
The unit has a display for fault signals and supports an external reset — useful for remote reset in unattended installations. Intrinsic device protection covers the soft starter itself against overtemperature and overcurrent, separate from the motor overload protection.