The Siemens 3RW4424-1BC34 is a SIRIUS soft starter — thyristor-based motor starting that ramps voltage to limit inrush current and mechanical shock on pumps, conveyors, fans, and compressors. Rated 81 A at 40 °C (73 A at 50 °C, 64 A at 60 °C), it handles motors up to that full-load current on a 400 V three-phase system. The 690 V insulation voltage (rated impulse withstand per IEC 60947-4-2, pollution degree 3) means it's built for industrial panels where line transients are a given. Control supply is 115 V at 50/60 Hz — a common voltage for North American and some European control transformers. The integrated bypass contact system shunts the thyristors after start, so the power semiconductors aren't carrying continuous load current; that cuts heat dissipation inside the panel and extends device life. Adjustable current limitation and motor overload protection are built in, meaning you don't need a separate overload relay for most applications.
Screw fixing to a vertical mounting surface — no DIN-rail clip on this frame size. Dimensions: 170 mm wide, 192 mm high, 270 mm deep. Clearance requirements: 100 mm above, 75 mm below, 5 mm at the sides — that 5 mm side gap is tight; adjacent devices or cable ducts need to respect it for airflow and arc flash containment. Main circuit terminals are box lugs accepting 2x (4...50 mm²) stranded or 2x (10...1/0 AWG) using both clamping points. Auxiliary and control circuit wiring uses screw-type terminals for 2x (0.5...2.5 mm²) solid or 2x (20...14 AWG). Maximum motor cable length is 500 m — sufficient for most distributed motor installations, but watch for capacitive charging current on long runs that could cause nuisance tripping of the overload protection.
Above 40 °C, derate linearly to 73 A at 50 °C and 64 A at 60 °C. If your panel ambient hits 50 °C, you lose about 10% of the rated capacity — factor that into motor selection or consider a larger frame. External reset allows remote fault clearing without opening the panel door. Display version for fault signal shows diagnostic codes locally. Intrinsic device protection covers overtemperature and phase-loss internally — no separate thermistor relay needed for the soft starter itself.