The Siemens 3RK4320-5JQ61-1BA3 is a SIRIUS MCU reversing motor starter designed for AS-Interface bus communication — it handles direction reversal and motor protection in a single enclosure, saving panel space over a contactor-plus-overload-plus-reversing-contactor stack. The 24 VDC control supply (20.4…26.4 V range) powers the onboard electronics and the AS-Interface transceiver, so the panel needs a regulated DC bus — not a raw rectified supply.
Brake control and I/O — what is actually onboard
This reversing starter includes a motor brake output rated for 400 V AC — the evidence confirms brake control at 400 V AC is present, while DC brake variants (24 V, 180 V, 500 V) are not. That means the unit directly drives an AC-fed holding brake without an external contactor, but if your motor has a DC brake rectifier you need a different variant. Two digital inputs are integrated for local start/stop or reset signals, reducing the need for separate I/O blocks. The main current circuit is three-pole, and short-circuit protection is designed for use with upstream circuit-breakers.