The Siemens SIRIUS 3RK4320-3BQ51-1BA3 is a reversing motor starter with integrated AS-Interface communication, built for 3-phase motor control up to 0.8 A in AC-3 duty at 400 V. The unit sits in a 245 mm wide × 215 mm high × 205 mm deep enclosure rated IP54, which means it's sealed against dust ingress and splashing water — fine for cabinet or machine-mounted locations in washdown zones, but not submersible.
Ratings that drive the fit
Motor current rating is 0.8 A at AC-3 (400 V) — that's the switching category for squirrel-cage motors: starting, stopping, and reversing under load. The same 0.8 A appears at AC at 400 V rated value, confirming the resistive and motor-duty curves align at this current level. For a 400 V line, that typically covers a motor in the 0.37–0.55 kW range depending on efficiency and power factor. Control supply is 20.4–26.4 V DC. The operating voltage range for the power circuit is 340–440 V AC. Frequency acceptance is 50/60 Hz. The unit includes a motor brake output for 400 V AC brake control, plus two digital inputs for local control or feedback. Short-circuit protection is handled by circuit-breakers (not fuses), and the electromechanical switching contacts give a clean, positive break — no semiconductor leakage. Ambient operating temperature spans –25 to +50 °C, so it's suitable for unheated plant floors or refrigerated environments. The AS-Interface protocol is supported natively — no gateway module needed for the bus connection.