433 A at 40 °C — the operating ceiling for full-load motor starting
The Siemens 3RW4444-2BC36 SIRIUS soft starter is rated 433 A at 40 °C ambient, which sets the maximum motor full-load current it can ramp up without exceeding its thermal limit.
Thyristor switching and inside-delta wiring
Built around thyristors for the main current path, this soft starter provides controlled voltage ramp starting to limit inrush current and mechanical shock to the driven load. The inside-delta circuit connection option reduces the current through the soft starter by a factor of √3 compared to standard in-line wiring — useful when the motor current exceeds the unit's rating but the soft starter can still handle the reduced phase current. Motor overload protection is integrated, so you can omit a separate overload relay in many installations. Adjustable current limitation lets you set the start current between 8% and the unit's full rating, matching the load's breakaway torque requirement.
Panel mounting and clearance requirements
Mounting is by screw fixing onto a vertical surface, with ±90° rotation and ±22.5° tilt allowance for panel layout flexibility. The footprint is 210 mm wide by 230 mm high, and the depth is 298 mm — that depth is the dimension to check for enclosure depth clearance, especially in shallow cabinets. Ventilation and safety spacing: 100 mm clearance required upwards, 75 mm downwards, and 5 mm at the sides. These gaps keep the heat from the thyristor stack from recirculating into the control electronics.
Field wiring and termination
Main circuit wiring accepts stranded conductors from 70 to 240 mm², finely stranded from 50 to 240 mm², and AWG/kcmil from 2/0 to 500 kcmil. For busbar connection, the main current circuit uses busbar connection points rather than cable lugs — a common preference in high-current switchgear where bus runs replace individual cables.
Sourced through authorized distribution channels. The unit carries pollution degree 3 per IEC 60947-4-2, suitable for industrial environments with conductive pollution.