The Siemens 3RK4320-3LQ54-0BA2 is a SIRIUS MCU (Motor Control Unit) — a compact, AS-Interface-bus-ready direct starter that integrates a contactor, overload relay, and communication interface in one housing. It's sized for motor loads up to 6.3 A in AC-3 duty at 400 V, with a bimetal overload trip characteristic in Class 10, so it protects standard induction motors during start-up without nuisance tripping on normal acceleration. This unit communicates over AS-Interface (the only bus protocol on board; no PROFINET or PROFIBUS DP), giving you two digital inputs for feedback from the line — limit switches, position sensors, or E-stop status — wired back to the AS-i master without a separate I/O block. The control supply is 20.4–26.4 VDC, and the main power circuit takes 340–440 VAC at 50/60 Hz. It includes a motor brake output component slot; short-circuit protection coordinates with upstream circuit-breakers.
The enclosure measures 205 mm deep, 245 mm wide, and 215 mm high, with an IP54 rating — sealed against dust ingress and splashing water, so it's suited for installation in industrial environments where washdown isn't routine but airborne particulates are present. Operating ambient temperature spans -25 to +50 °C, with a maximum switching frequency of 80 operations per hour. The device is a three-pole direct starter (no reversing contactor inside), so for a reversing or two-speed application you'd pair two of these units and handle the interlocking in the AS-i master logic.