What the 1200 A rating means for your motor load
The Siemens 3RW4455-6BC46 is a SIRIUS soft starter rated 1200 A at 40 °C — that's the full-load current it handles in standard duty, not a surge rating. The 690 V insulation voltage (rated value) means it's built for 400 V and 480 V line supplies with headroom; pollution degree 3 per IEC 60947-4-2 confirms it tolerates the conductive dust and humidity typical of industrial enclosures without conformal coating. Inside-delta wiring is supported, which cuts the current seen by each thyristor pair to 58% of the line current — useful for squeezing a 1200 A motor start out of a physically smaller unit. The integrated bypass contact system closes after the start ramp, taking the thyristors out of the circuit so they don't dissipate heat during continuous run; that keeps the enclosure cooler and extends the semiconductor life.
Mounting and wiring — what fits in the panel
The unit measures 640 mm high by 510 mm wide by 290 mm deep, with screw fixing to the mounting surface. It's not a DIN-rail snap-on; plan for a dedicated backplate. Clearance requirements: 100 mm above, 75 mm below, 5 mm at the sides. For storage, the range is -25 to +80 °C; during operation the ambient limit is 60 °C. Main current circuit connection is via busbar, not cable lugs — order the appropriate busbar kit separately. The main contact terminals accept 2/0 to 500 kcmil or 70 to 240 mm² stranded, 50 to 240 mm² finely stranded. Auxiliary and control wiring uses screw-type terminals accepting 2x (0.5 to 2.5 mm²) solid or 2x (20 to 14 AWG). Maximum motor cable length is 500 m; beyond that, reflected wave spikes on long leads may need an output reactor.
Control and protection features
Motor overload protection and intrinsic device protection (thyristor overtemperature, phase imbalance, etc.) are built in — no separate overload relay needed. Adjustable current limitation lets you set the start current between 8% and 100% of the rated motor current. An external reset input allows remote fault clearing, and the display shows fault codes directly. A motor brake output is included as a product component, so you can control the brake coil through the soft starter without an extra contactor. The operating frequency range is 50 to 60 Hz, with the control supply rated 230 V at both 50 Hz and 60 Hz. The minimum load is 8% of the rated current.