The Siemens 3RA1220-1KB25-0BW4 is a reversing combination starter in the SIRIUS family, frame size S0, rated for 9-12.5 A with a 24 VAC control voltage. It integrates a reversing contactor pair and a motor-protective circuit breaker into one FastBus-mount unit, so it handles forward/reverse motor control and short-circuit/overload protection in a single panel footprint. The UL File E156943 listing means it is accepted for North American installations under UL 508A.
The 9-12.5 A range covers small reversing loads like conveyor drives, pump reversals, or actuator motors. The 24 VAC control coil is standard for many PLC-driven panels, but note it is AC — if your cabinet runs 24 VDC control, this coil will not hold in; you need the DC-rated variant. The FastBus mount clips directly onto the SIRIUS bus system, which saves wiring time compared to point-to-point connections between separate contactors and breakers.