Current ratings and thermal derating
The Siemens SIRIUS 3RW3455-0DC35 is a soft starter for standard applications, rated 121 A at 40 °C in a standard circuit configuration. That current rating drops to 99 A at 50 °C and 73 A at 60 °C, so the enclosure ventilation and ambient temperature directly govern the motor current this unit can handle continuously. The operating voltage range is 400... 600 V at 50/60 Hz, covering common 400 V and 480 V industrial supplies.
Inside-delta connection unlocks higher power
Wired in an inside-delta configuration, the same unit handles 75 kW at 40 °C versus 45 kW in a standard circuit — a 67 % power gain from the same hardware. At 50 °C the inside-delta rating is 100 hp compared to 50 hp standard. This matters when the motor is physically larger than the soft starter's standard rating, because the inside-delta connection places the thyristors in the motor windings rather than the supply lines, reducing the current each device sees.
The main current circuit connects via busbar connections, while the auxiliary and control circuit uses screw-type terminals. Mounting is screw fixing — no DIN-rail clip — so plan for panel-mounting with the 216 mm width, 356 mm height, and 187 mm depth. The control supply voltage is AC/DC at 115 V, 50/60 Hz. Three NO auxiliary contacts are provided; no NC or CO contacts are fitted.