617 A at 40 °C — the current rating that drives the selection
The 3RW4446-2BC35 is a Siemens SIRIUS soft starter rated for 617 A at a 40 °C ambient, with a 690 V insulation voltage ceiling. This is the headline current for motor starting duty — it sets the maximum motor FLA the unit can handle in a standard panel environment. Above 40 °C, the current derates to 546 A at 50 °C and 485 A at 60 °C, so enclosure cooling or a larger frame may be needed if the ambient runs hot. The unit operates on 50 or 60 Hz mains and accepts a 115 V control supply at both frequencies — no separate control transformer tap for 50 vs 60 Hz.
Thyristor switching with adjustable current limit and inside-delta capability
Thyristor-based design with adjustable current limitation means you dial in the starting current between 8% and the full rating, controlling inrush on conveyors, pumps, or compressors. Motor overload protection is integrated, so a separate overload relay is not needed in most schemes — the soft starter handles the thermal model of the motor. Inside-delta circuit support allows the soft starter to be wired in the motor's delta loop, reducing the current the unit must carry by 42% compared to standard in-line wiring. This is a common trick on larger motors to save panel space and cost, but it requires the motor leads to be brought back to the panel.
Mounting and connection — panel layout constraints
Dimensions are 230 mm high, 210 mm wide, 298 mm deep. Mounting is by screw fixing with a vertical mounting surface that can be rotated ±90° or tilted ±22.5° front/back — useful for tight enclosures or odd orientations. Clearance requirements: 100 mm upwards, 75 mm downwards, 5 mm at the sides. Main circuit connections accept stranded cable 70–240 mm², finely stranded 50–240 mm², or kcmil equivalents: 2/0–500 kcmil using both clamping points, 250–500 kcmil using the back clamping point, and 3/0–600 kcmil using the front clamping point. Busbar connection is also supported. Auxiliary contacts accept 24–16 AWG, and solid control wires 0.25–1.5 mm².