Headline rating — 1351 A at 40 °C, what it means for motor sizing
The 3RW4456-2BC46: The 1351 A at 40 °C is the continuous current rating in standard ambient. For a 690 V insulation class motor at 400 V, that translates to roughly 900 kW — but the actual motor FLC determines the soft starter frame, not the other way around. Derate to 1200 A at 50 °C and 1065 A at 60 °C if the cabinet ambient runs hot; the derating starts above 40 °C. The minimum load is 8% of the rated current — so it won't regulate down to a fractional-horsepower motor. Keep that in mind if the application is a small pump on the same line.
Integrated bypass — one less contactor to stock
The integrated bypass contact system means the soft starter's thyristors are shorted out once the motor is up to speed. That's one less external bypass contactor to buy, wire, and shelf-spare. The bypass also cuts heat dissipation in the cabinet during run — the thyristors only carry current during the start ramp. Inside-delta circuit wiring is supported — if the motor is delta-connected and you wire the soft starter in the delta legs, the per-phase current through the unit is roughly 58% of the line current. That can let you downsize the soft starter frame for the same motor, but the wiring gets more involved.
Mounting and panel fit — screw-fixed, not DIN-rail
Clearance: 100 mm above, 75 mm below, 5 mm at the sides. The side clearance is tight — adjacent devices or cable ducts need to respect that for cooling airflow. Main circuit cables: stranded 70-240 mm² or finely stranded 50-240 mm². For North American wire sizes, that's 2/0 to 500 kcmil. The auxiliary and control circuit terminals are spring-loaded, accepting 0.25-1.5 mm² solid or 24-16 AWG. No screw torque to check on the control wiring.
Protection and diagnostics — onboard display, adjustable current limit
Motor overload protection and intrinsic device protection are built in — the soft starter monitors its own thyristor temperature and the motor current. The adjustable current limitation lets you set the start current between 100% and, presumably, some lower percentage (the spec doesn't give the ceiling, but typical SIRIUS units go to about 400% of FLC). Fault signals show on the onboard display — no need to wire a separate HMI for basic diagnostics. External reset is available for remote clearing after a trip. The motor brake output is a product component — if the application has a DC brake, the soft starter can control it directly. Wire length maximum is 500 m from the unit to the motor; beyond that, voltage drop and reflected wave issues start to matter.
Sourced through independent distribution against an RFQ. The SIRIUS brand is Siemens' standard industrial soft starter line, widely specified and cross-referenced.