What this control unit does in the starter assembly
The 3RW4774-6SB40: This is the 230 V control unit for the Siemens 3RW4074 soft starter in Size S12 — it's the logic and firing board that manages the SCR gating, ramp timing, and bypass contactor sequence. The screw terminals on this unit accept the control wiring from the PLC or start/stop station; the power section (thyristor module and bypass) is a separate assembly that mates to this board.
Compliance and documentation
The part carries the standard Siemens declaration of conformity for the 3RW4 series; the product designation on the nameplate reads "Control unit" — match this against the PO line description to avoid warehouse mix-ups with the power module.