1680 A soft starter with integrated bypass for heavy motor starts
The Siemens SIRIUS 3RW4458-6BC44 is a soft starter rated 1 680 A at 40 °C, with an insulation voltage of 690 V and an operating frequency of 50... 60 Hz. That current rating governs motor starts up to that full-load amp level in a standard 40 °C enclosure — derate to 1 472 A at 50 °C and 1 316 A at 60 °C if your panel runs hot. The integrated bypass contact system takes the thyristors out of circuit after start, so you don't pay continuous conduction losses across the silicon. This is a SIRIUS-series unit designed for screw-fixing to a vertical mounting surface, rotatable ±90° and tiltable ±22.5° front-to-back. The 510 mm width × 640 mm height × 290 mm depth footprint means it fills a full panel section — plan the gland plate and busbar clearance accordingly.
Protection and control features for demanding motor loads
Motor overload protection and intrinsic device protection are built in — no separate overload relay needed upstream for the soft starter itself. The adjustable current limitation lets you set the start current between 8% and 100% of the motor FLA, which is useful for soft-starting conveyors or pumps that need a controlled ramp without mechanical shock. Minimum load is 8%, so it won't drop out on lightly loaded motors. An external reset input and a display for fault signals make commissioning and troubleshooting straightforward. The inside-delta circuit wiring configuration reduces the current through the thyristors by a factor of √3 compared to standard in-line connection — useful for squeezing higher motor ratings from the same device frame. A product component motor brake output is included, so this unit can directly control a DC brake on the motor shaft without an external contactor. The maximum wire length to the motor is 500 m, which covers most plant-floor runs.
Termination and wiring — busbar primary, screw terminals for auxiliaries
The main current circuit connects via busbar connection — expect to run copper bars rather than cable tails for the 1680 A feed. Solid conductors accepted are 2x (0.5... 2.5 mm²) for the auxiliary and control circuit, which uses screw-type terminals. Stranded main conductors range from 70... 240 mm², finely stranded from 50... 240 mm², and AWG/kcmil equivalents are 2/0... 500 kcmil. Clearance requirements: 100 mm upwards, 75 mm downwards, 5 mm at the side. Storage temperature range is -25... +80 °C; during operation the ambient limit is 60 °C.