280 A at 40 °C — what it means for the motor circuit
The 3RW4074-2BB34: This SIRIUS soft starter is rated 280 A at 40 °C ambient, which translates to a motor full-load current ceiling of about 280 A in a 40 °C panel. The adjustable current limitation lets you set the starting current below the motor's locked-rotor value, reducing mechanical shock and voltage sag on the line. Motor overload protection is built in, so a separate overload relay isn't needed in most installations.
Panel fit and mounting constraints
The unit measures 230 mm high by 160 mm wide by 278 mm deep and mounts via screw fixing. It's a size S12 frame — expect a substantial footprint; plan for the busbar connection on the main circuit and the cable entry clearance: 100 mm above, 75 mm below, 5 mm at the sides. Mounting position is flexible: with an additional fan, the unit can be mounted vertically with up to ±90° rotation or ±22.5° tilt; without the fan, the tilt range narrows to ±10°.
Wiring and connection details
Main circuit cables: stranded 70–240 mm² or finely stranded 50–240 mm², or AWG 2/0–500 kcmil for the main contacts. The back clamping point accepts 250–500 kcmil, the front clamping point 3/0–600 kcmil. Maximum motor cable length is 300 m. The unit includes thyristors and supports external reset. Minimum load is 20% of the rated current — don't use it on a motor drawing less than about 56 A at 40 °C or the soft starter may not regulate properly.