The Siemens 3RW4056-2BB45 is a SIRIUS soft starter, size S6, designed to ramp induction motors up to speed and limit inrush current during start. It uses thyristors in the main circuit to control voltage to the motor, reducing mechanical shock on couplings and driven loads. Built-in motor overload protection means you don't need a separate overload relay for the motor branch circuit. The adjustable current limitation lets you dial in the start current to match the load — useful for conveyors, pumps, or compressors that need a soft start without tripping upstream protection.
Mounts via screw fixing to a vertical panel surface. The 198 mm height, 120 mm width, and 250 mm depth give it a substantial footprint — plan for that depth when laying out the enclosure depth. Clearance requirements: 100 mm above, 75 mm below, and 5 mm at the sides. With an additional fan, the mounting surface can rotate ±90° or tilt ±22.5° front-to-back; without the fan, rotation is limited to ±10° and tilt to ±10°. Main circuit connections are via busbar or cable lugs. Stranded cable range is 2x (25 to 120 mm²); finely stranded accepts 2x (16 to 95 mm²). Solid wire connections are 2x (0.25 to 1.5 mm²) — that's for the control wiring, not the power legs. The front and back clamping points each accept 6 to 2/0 AWG; using both clamping points together maxes out at 2x 1/0 AWG. For main contacts, the range is 4 to 250 kcmil.
Rated operational current drops with ambient temperature: 162 A at 40 °C, 145 A at 50 °C, and 125 A at 60 °C. Derating starts above 40 °C. Insulation voltage is rated 600 V, and the operating frequency is 50 to 60 Hz at 230 V. Minimum load is 20% of the rated current — below that, the soft starter may not regulate properly. Maximum motor cable length is 300 m. The unit is not configured for inside-delta wiring; it's a standard in-line soft starter.