1200 A at 40 °C — the rating that sizes the motor circuit
The 3RW4455-2BC34: That 40 °C baseline is the standard industrial panel ambient — if your enclosure runs hotter, the available current drops by about 11 % per 10 °C rise. Insulation voltage is 690 V, giving headroom on 400/480 V systems. The unit operates on 50/60 Hz lines, so it's a single SKU for global installs. Pollution degree 3 per IEC 60947-4-2 means it's rated for the conductive dust and humidity you get in a typical industrial panel — no derating for dirty environments.
Integrated bypass — less heat, smaller cabinet
An integrated bypass contact system shorts the thyristors once the motor is up to speed. That means the soft starter's heat sink only dissipates power during the start ramp — during run, the bypass carries the current with near-zero loss. This keeps the cabinet cooler and lets you size the ventilation for starting duty, not continuous full-load heat. Inside-delta circuit wiring is supported, which reduces the current through each soft starter phase to 58 % of the line current. If you're starting a delta-wound motor, this can drop the required unit rating by nearly half — useful for squeezing a larger motor into an existing starter frame.
Mounting and wiring — what fits in the panel
Dimensions are 640 mm high × 510 mm wide × 290 mm deep. Screw fixing — no DIN-rail clip; plan for four mounting points on the backplate. Clearance: 100 mm above, 75 mm below, 5 mm at the sides. That 100 mm top gap is for cable bending radius and airflow; don't pinch it. Main current circuit uses busbar connection — expect flat copper bars, not cable lugs. The auxiliary terminals are spring-loaded — strip and push, no screwdriver needed. Maximum motor cable length is 500 m — long enough for most plant layouts, but if you're pushing a remote motor past that, you'll need an output reactor.
Protection and control features
Motor overload protection and intrinsic device protection are both built in. Adjustable current limitation lets you set the start current between 8 % and 100 % of the rated value — the minimum load threshold is 8 %, so it handles lightly loaded conveyors and pumps without nuisance tripping. External reset input and a display for fault signals are standard. The unit also includes a motor brake output component — if your application has a mechanical brake, this saves an external relay. Storage temperature range is -25 to +80 °C; operating ambient max is 60 °C. The derating temperature threshold is 40 °C — above that, follow the derating curve in the manual.
Lifecycle and sourcing — active, quoted to order
Lifecycle stage is marked 'current' — this is an active-production part from Siemens. The 3RW4455-2BC34 is a standard catalog item in the SIRIUS family. Confirm your BOM line against the 1200 A rating and 690 V insulation before ordering.