1200 A at 40 °C — sizing this soft starter for the motor
The 3RW4455-2BC44: Rated 1200 A at 40 °C ambient, this SIRIUS soft starter handles large motor loads — think pumps, conveyors, or compressors in the 600–800 kW range depending on voltage and service factor. Derate to 1065 A at 50 °C and 954 A at 60 °C — the 40 °C derating temperature means the full 1200 A is only available below that threshold; above it, the current ceiling drops. The 690 V rated insulation voltage (IEC 60947-4-2) and pollution degree 3 suit industrial panels where conductive dust or humidity is present — common in heavy manufacturing.
Integrated bypass and inside-delta wiring — what it means for the panel
An integrated bypass contact system means the thyristors are shorted out after start, eliminating heat dissipation from the silicon during run — the panel's cooling requirement drops significantly. Inside-delta circuit capability lets you wire the soft starter in the delta leg of a six-lead motor, reducing the unit's current rating requirement to 58% of the motor FLA — useful for retrofitting into existing motor circuits without upsizing the starter. Main current circuit connects via busbar (not cable lugs), and the main contacts accept 2/0 to 500 kcmil — expect to terminate with busbar kits, not compression lugs.
Mounting and clearances — fitting the 640 mm tall unit
At 640 mm height, 510 mm width, and 290 mm depth, this is a floor-mount or large enclosure unit — not a DIN-rail candidate. Fastening is by screw fixing, not snap-on. Mounting position allows vertical surface with +/-90° rotation and +/-22.5° tilt forward/back — the enclosure layout must accommodate the swing arc, not just the footprint. Minimum clearances: 100 mm above, 75 mm below, 5 mm at the sides — the top clearance is for cable entry and heat plume; the 5 mm side gap is tight, so adjacent devices must not block ventilation.
Protection and control features built in
Motor overload protection is integrated — no separate overload relay needed in the power circuit. Intrinsic device protection covers the thyristors against over-temperature and over-current. Adjustable current limitation lets you set the start current between 8% and 100% of the unit's rating — the 8% minimum load means it can soft-start very lightly loaded motors without hunting. External reset input and a display for fault signals give the panel builder a local HMI point without opening the enclosure door. A motor brake output component is included — if the motor has a DC brake, this starter can control it directly, saving a separate contactor.
Cable sizing and connection notes
Main circuit power cables: stranded 70 to 240 mm² or finely stranded 50 to 240 mm² — the finely stranded range starts lower because the finer strands fill the lug better at smaller cross-sections. Maximum motor cable length is 500 m — beyond that, capacitive charging current from the cable can interfere with the thyristor firing or cause nuisance trips on the overload detection.