Continuous current and derating — what 280 A really means for the motor
The 3RW4074-6BB45: Rated 280 A at 40 °C, this soft starter handles a motor of roughly 160 kW at 230 V — but only if the enclosure ambient stays at or below 40 °C. At 50 °C the continuous rating drops to 248 A; at 60 °C it falls to 215 A. The derating temperature threshold is 40 °C, so any panel with internal temperature rise above that must be factored into the motor full-load current. Pollution degree 3 per IEC 60947-4-2 means the unit tolerates conductive dust and humidity typical of industrial floors — no need for a sealed enclosure unless washdown is present.
Termination and wiring — main circuit and control
Main circuit termination accepts stranded cable 70–240 mm² and finely stranded 50–240 mm², plus busbar connection. For North American wire sizes, the front clamping point takes 3/0–600 kcmil and the back clamping point 250–500 kcmil. Using both clamping points accepts min. 2x 2/0 to max. 2x 500 kcmil. Maximum motor cable length is 300 m — beyond that, capacitive charging current may cause nuisance tripping or reduce the soft starter's ability to limit inrush. Mounting is screw fixing. The S12 frame measures 160 mm wide, 230 mm high, 278 mm deep. Clearances: 100 mm upward, 75 mm downward, 5 mm at the sides.
Protection and control features
Built-in motor overload protection and intrinsic device protection eliminate the need for a separate overload relay in most installations. Adjustable current limitation lets you set the starting current between 20% and 100% of the soft starter's rated current — useful when starting into a limited supply transformer or generator. Minimum load is 20%. External reset input allows remote fault clearing from a PLC or pushbutton station. Thyristor-based with inside-delta circuit not supported. Operating frequency is 50–60 Hz; rated insulation voltage is 600 V.