SIRIUS soft starter for motor starting duty
The 3RW4038-2TB04: An integrated bypass contactor switches the motor to line power once at speed, eliminating thyristor conduction losses during run — the soft starter then acts as a pass-through, not a continuous heat source in the panel.
Current derating and panel integration
Rated 72 A at 40 °C, the 3RW4038-2TB04 derates to 62 A at 50 °C and 60 A at 60 °C — the derating temperature threshold is 40 °C, so any ambient above that reduces the continuous motor current the unit can handle. Mounting is screw or snap-on to DIN rail; the unit measures 55 mm wide by 160 mm high by 170 mm deep, with 60 mm clearance required above and 40 mm below for airflow. Pollution degree 3 per IEC 60947-4-2 means the soft starter is rated for industrial environments where conductive pollution or dry non-conductive pollution that becomes conductive due to condensation is expected — no additional conformal coating required for typical panel duty.
Wiring and protection features
Built-in motor overload protection and intrinsic device protection are standard, with adjustable current limitation and an external reset input for remote fault recovery. The minimum load is 20 % of the rated current, and the maximum motor cable length is 300 m — relevant when the starter is remote from the motor.