Continuous current derating — the real thermal limit
The 3RW4073-6BB35 is rated 230 A at 40 °C, 205 A at 50 °C, and 180 A at 60 °C. That 50 A drop from 40 to 60 °C means the panel ambient temperature directly sets the motor current the starter can carry continuously — if the enclosure runs at 50 °C, you lose about 11 % of the headline rating. Derating temperature is 40 °C — above that, the thyristor junction temperature climbs faster than the case can shed heat. In a confined panel with other heat sources, budget for the 60 °C figure unless forced ventilation is fitted.
Termination and wiring — busbar connection, dual clamping
Main circuit termination is busbar connection, not cable lugs. The front clamping point accepts 3/0 to 600 kcmil; the back clamping point takes 250 to 500 kcmil. Using both clamping points allows min. 2x 2/0, max. 2x 500 kcmil — useful for paralleling conductors on high-current runs. The control terminals are separate from the power bus, so the wiring tray stays clean.
Mounting and panel clearance
Mounting is screw fixing, not DIN rail. The envelope is 160 mm wide, 230 mm tall, 278 mm deep — plan for a backplate that accommodates the depth plus cable bend radius. Clearance above the unit is 100 mm, below 75 mm, at the side 5 mm. Mounting position allows ±90° rotation with vertical surface when an additional fan is fitted, or ±10° rotation without fan. Tilt limits are ±22.5° with fan, ±10° without. For a standard vertical panel, no special orientation is needed.
The SIRIUS family is Siemens' standard soft starter line, size S12. Pollution degree 3 per IEC 60947-4-2 means it is rated for industrial environments with conductive pollution — no need for additional conformal coating in most panel builds.