Rated current and thermal derating — sizing for the real ambient
The 3RW4075-2BB44 is rated 356 A at 40 °C ambient. The derating temperature is 40 °C — above that, the continuous current must be reduced per the curve. If the panel ambient runs at 50 °C, size the motor FLA against 315 A, not the headline 356 A.
Mounting and panel integration — size S12 constraints
Physical dimensions: 230 mm height, 160 mm width, 278 mm depth. Fastening method is screw fixing — no DIN-rail clip on this size. Mounting position allows vertical surface with ±10° tilt without additional fan; with the optional fan, ±90° rotation and ±22.5° tilt front-to-back. Clearance requirements: 100 mm upwards, 75 mm downwards, 5 mm at the sides. The main circuit connection accepts busbar or cable: stranded 70–240 mm², finely stranded 50–240 mm², or 2/0–500 kcmil.
Protection and control features — what the thyristor stack delivers
Thyristor-based firing with adjustable current limitation — set the starting current between 20% and the rated current to match the load's breakaway torque without mechanical shock. Minimum load is 20%; below that the soft starter may not trigger reliably. Integrated motor overload protection and intrinsic device protection — the soft starter monitors both the motor and its own thyristor junction temperature. External reset input allows remote fault clearing. Maximum motor cable length is 300 m — beyond that, reflected wave voltage spikes may damage the motor insulation. Inside-delta circuit is not supported — this is a standard in-line configuration. Insulation voltage rated 600 V.