The Siemens 3RA1125-1KA25-1BB4 is a SIRIUS nonreversing combination starter in frame size S0, rated for 9-12.5 A with a 110 VDC control voltage. It integrates the contactor and overload relay into one DIN-rail or panel-mount unit, saving panel space and wiring time on motor control circuits up to that current range. The 110 VDC control coil means this starter is a direct fit for DC control buses common in industrial panels — no separate rectifier or AC coil conversion needed. The auxiliary contact block includes one SPDT (NO/NC) contact from the MSP and one additional NO contact from the contactor, giving you feedback and status signals for the PLC or HMI without adding a separate aux block.
Frame size S0 defines the physical footprint and the maximum thermal overload relay range. If your panel layout is already planned for S0, this starter drops into the same DIN-rail cutout and busbar system as other SIRIUS S0 components.