The Siemens 3RA1225-0KB23-1BB4 is a reversing combination starter in the SIRIUS S0 frame, rated for 0.9-1.25 A with a 110 VDC control voltage. It integrates a reversing contactor pair, overload relay, and short-circuit protection into one DIN-rail or panel-mount package — a common choice for controlling small reversing motor loads like conveyor drives or actuator gates in IEC panels.
The 0.9-1.25 A current range sets the motor FLA it can handle — size the overload relay dial within that window to match the motor nameplate. The 110 VDC control voltage means the coil pulls in on a 110 VDC supply; verify your control transformer or DC power supply delivers that, not 110 VAC, because the coil is DC-rated and an AC supply will not hold it in (or may damage it). The S0 frame size determines the mounting footprint and busbar spacing — it shares the same 45 mm width and DIN-rail clip pattern as other S0 SIRIUS gear, so it swaps into existing S0 panels without re-drilling. The auxiliary contact configuration includes one SPDT NO/NC contact on the MSP (motor starter protection) block plus one NO front-mount contactor auxiliary — enough for a run-status signal to a PLC or a seal-in circuit for the reversing logic. The UL file E156943 Vol.1 Sec.14 confirms UL listing for North American installations, so it passes a panel shop inspection without a separate UL component review.