The Siemens 3RK4320-3MQ54-1BA3 is a SIRIUS motor starter MCU designed for AS-Interface bus communication — a reversing starter with electromechanical switching contacts, rated 8 A at AC-3, 400 V (motor duty) and protected by a CLASS 10 bimetal overload relay. It carries a DC control supply (20.4... 26.4 V) and includes a motor brake output for 400 V AC, making it suitable for reversing applications that need a brake release on a conveyor or hoist. The IP54 enclosure means it is dust-protected and splash-resistant — fine for a control cabinet or a protected machine-mount location, but not for washdown zones.
At AC-3, 400 V the rated operational current is 8 A — that is the motor-switching current for a 3-phase induction motor up to roughly 4 kW (depending on efficiency and duty). The operating voltage range is 340... 440 V, 50/60 Hz. Ambient temperature during operation is -25... +50 °C. The unit measures 245 mm wide × 215 mm high × 205 mm deep — a substantial footprint for a reversing starter with integrated brake output and AS-Interface electronics.
AS-Interface integration and I/O
This starter communicates exclusively over AS-Interface (no PROFIBUS DP, no PROFINET). It has 2 digital inputs on board, which can be used for local pushbuttons or limit switches without an extra I/O block. The brake control output is rated for 400 V AC, so it switches an external brake coil directly — no intermediate relay needed for that voltage class.