Current rating and thermal derating — the real operating envelope
The 3RW4453-2BC44: The derating temperature threshold is 40 °C — above that, the continuous current drops linearly per the datasheet curve. For a panel with an internal ambient of 50 °C, budget 856 A as the usable ceiling; the 60 °C figure (759 A) applies only if the enclosure ventilation keeps the air around the unit below that limit. The insulation voltage is rated 690 V, with an operating frequency range of 50 to 60 Hz.
Integrated bypass and inside-delta topology
An integrated bypass contact system is built into the unit — once the motor reaches full speed, the thyristors are shorted out, eliminating heat dissipation from the semiconductor stack during continuous run. This means the enclosure thermal budget is set by the bypass contactor losses, not the silicon junction temperature. The unit supports inside-delta circuit wiring, which connects the soft starter in the delta legs of a six-lead motor. This reduces the current through each thyristor to 58% of the line current, effectively extending the current range of the unit without increasing the semiconductor die size. Verify the motor has six accessible leads before specifying this topology.
Protection functions and control features
Motor overload protection is integral — the unit monitors motor current and trips on overload without requiring an external overload relay. Intrinsic device protection covers the thyristors against over-temperature and over-current, and the adjustable current limitation lets you set the start current between 8% and 100% of the rated current. An external reset input is provided, allowing remote reset of the fault condition from a PLC or pushbutton station. The display shows fault codes directly on the unit, reducing troubleshooting time. A motor brake output is included as a product component — this can control a DC injection brake or mechanical brake coil without an additional interface relay.
Mounting, wiring, and clearance dimensions
The unit measures 640 mm high, 510 mm wide, and 290 mm deep. Fastening is by screw fixing (not DIN-rail clip) — the enclosure backplate must have drilled and tapped holes matching the mounting pattern. The mounting position allows vertical surface mounting with +/-90° rotation and +/-22.5° tilt forward/backward, giving flexibility in panel layout. Minimum clearance requirements: 100 mm above, 75 mm below, and 5 mm at the sides. Maximum motor cable length is 500 m — beyond this, capacitive charging current may cause nuisance tripping or thyristor misfiring. The pollution degree is 3 per IEC 60947-4-2, meaning the unit is suitable for industrial environments with conductive dust or occasional condensation.
Environmental limits and storage conditions
During operation, the ambient temperature must not exceed 60 °C. Storage temperature range is -25 to +80 °C — this applies to the unit in its original packaging, not installed in a panel. The product brand is SIRIUS, and the product designation is 'Soft starter' per the Siemens catalog.