The Siemens 3RK4320-3FQ54-1BA2 is a SIRIUS MCU reversing motor starter designed for AS-Interface bus communication. It integrates a reversing contactor pair, a CLASS 10 bimetal overload relay, and short-circuit protection via circuit-breakers into a single 245 mm wide enclosure. The 2 A AC-3 rating at 400 V means it switches small reversing motor loads — conveyors, diverters, gate drives — up to that current in standard 50/60 Hz networks. The 24 VDC control supply (20.4...26.4 V) keeps it on the same low-voltage bus as the AS-Interface network and PLC outputs.
The 2 A AC-3 rating is the motor-switching current, not the resistive (AC-1) rating; if your motor full-load amps exceed 2 A at 400 V, this starter is undersized. The IP54 enclosure keeps out dust and splashing water, so it suits panel-mount or machine-mounted locations that aren't directly hosed down.
AS-Interface integration and I/O
This starter communicates exclusively via AS-Interface protocol — no PROFIBUS or PROFINET onboard. It provides 2 digital inputs for local sensors (e.g., limit switches or emergency stops wired directly to the starter), reducing separate I/O module count. The reversing design means a single unit handles forward/reverse control of a motor, with mechanical and electrical interlocking built in. The 340...440 V operating voltage range covers 400 V nominal supplies with typical tolerance.