The Siemens 3RK4320-3FQ54-1BA3 is a SIRIUS MCU motor starter — a compact, reversing starter designed for AS-Interface bus communication. It integrates a motor-protective function (bimetal, CLASS 10 trip class) with electromechanical switching contacts, all in one 205 x 245 x 215 mm enclosure rated IP54. The reversing configuration means it can switch a motor's direction without external contactors, which saves panel space and wiring on bidirectional drives like conveyors or positioning slides.
Rated at 2 A in AC-3 duty at 400 V, this starter handles a 3-phase induction motor up to that current — roughly 0.75 kW at 400 V. The control supply is 24 V DC nominal (20.4 to 26.4 V range), and the main circuit operating voltage spans 340 to 440 V AC at 50/60 Hz. It includes a motor brake output (400 V AC), so it can directly control a brake coil on the motor shaft, eliminating a separate brake rectifier or contactor.
AS-Interface integration and I/O
This unit communicates via AS-Interface protocol — not PROFIBUS or PROFINET — so it belongs on an AS-i network segment, typically tied to a gateway that bridges to a higher-level fieldbus. It provides 2 digital inputs for local sensors (e.g., limit switches or e-stops) and reports motor status back over the bus. The IP54 rating means it's protected against dust ingress and splashing water, suitable for most industrial environments but not for direct washdown.