SIRIUS 3RW4444-6BC46 soft starter — 433 A, thyristor-switched
The Siemens 3RW4444-6BC46 is a SIRIUS-brand soft starter rated 433 A at 40 °C, 372 A at 50 °C, and 320 A at 60 °C, operating on 50/60 Hz line frequency with a rated insulation voltage of 690 V. It uses thyristor switching for the main current circuit and supports inside-delta wiring, which reduces the current draw through the device by roughly 58% compared to standard in-line wiring — a key consideration when sizing upstream protection. The minimum load threshold is 8% of the motor's full-load current, so it handles lightly loaded starts without nuisance tripping.
Dimensions, mounting, and wiring
The unit measures 230 mm high, 210 mm wide, and 298 mm deep, mounting via screw fixing on a vertical surface. Clearance requirements: 100 mm above, 75 mm below, 5 mm at the sides — the side gap is tight, so plan for adequate ventilation in a crowded enclosure. Main current connections accept busbar or cable: stranded 70–240 mm², finely stranded 50–240 mm², or AWG 2/0–500 kcmil. Auxiliary contacts accept 2x (0.5–2.5 mm²) solid or 2x (20–14 AWG). The back clamping point handles 250–500 kcmil; the front clamping point handles 3/0–600 kcmil. Maximum wire length is 500 m — relevant for remote motor installations where voltage drop must be checked.
Storage temperature range is -25 to +80 °C; during operation the ambient limit is 60 °C. Derating starts above 40 °C, so the 433 A rating applies only up to that point; at 50 °C it drops to 372 A, and at 60 °C to 320 A. The soft starter includes an external reset input and a display for fault signaling, supporting on-device diagnostics without needing a separate HMI. Intrinsic device protection is built in, covering the thyristors against over-temperature and short-circuit conditions.