The Siemens 3RW4074-6BB44 is a SIRIUS soft starter, Size S12, designed to ramp up and protect three-phase induction motors. It uses thyristors to control voltage during start, reducing mechanical shock and inrush current. The 230 V rated voltage at 50/60 Hz is the line voltage it's built for. It includes motor overload protection and adjustable current limitation, so you can set the start current profile to match the load. The minimum load is 20%, meaning it needs at least that much motor current to regulate properly — don't use it on a motor that's massively oversized for the load. An external reset input is available for remote fault clearing. Intrinsic device protection covers the soft starter itself against overtemperature and other internal faults.
This is a screw-fixing unit, not a DIN-rail snap-on. The dimensions are 230 mm high, 160 mm wide, and 278 mm deep — that's a substantial footprint, so plan your panel layout accordingly. The main current circuit uses busbar connection, with wire ranges for stranded (70 to 240 mm²) and finely stranded (50 to 240 mm²) conductors. For the main contacts in kcmil, it accepts 2/0 to 500 kcmil using both clamping points, with a back clamping point range of 250 to 500 kcmil and a front clamping point range of 3/0 to 600 kcmil. Solid wire for auxiliary contacts is 2x (0.5 to 2.5 mm²). The mounting position is flexible: with an additional fan, it can be mounted on a vertical surface with +/-90° rotation or +/-22.5° tilt; without a fan, the rotation is limited to +/-10°. Clearance requirements: 100 mm upwards, 75 mm downwards, and 5 mm at the side. The maximum wire length to the motor is 300 m — keep that in mind for long cable runs.