The Siemens 3RV1901-1DA00-0FQ0 is an auxiliary switch in a transverse mounting configuration, rated at 1 W, designed for use with circuit-breakers in the S00 through S3 frame sizes. It is a current-production item per the manufacturer's lifecycle stage.
The 1 W rating is the switching capacity for the auxiliary contact — it governs the maximum load the switch can break in a control circuit. For a typical 24 VDC PLC input, that translates to roughly 40 mA; for a 230 VAC signal, about 4 mA. The transverse mounting orientation means the switch actuates perpendicular to the breaker's operating mechanism, which affects the physical clearance inside the enclosure — verify the swing arc against adjacent components. Compatibility spans the S00, S0, S1, S2, and S3 frame sizes of the 3RV series motor starter protectors and circuit-breakers. That covers the majority of Siemens motor feeder applications from fractional-horsepower up to about 30 kW at 400 VAC. The switch clips onto the left or right side of the breaker housing; no additional mounting hardware is required.
For BOM freeze or PCN-watch purposes, this auxiliary switch carries no known replacement or supersession. It is the transverse variant of the standard auxiliary switch for the 3RV1 family; the longitudinal version (3RV1901-1DA00-0FQ1) uses the same contact block but a different actuation lever, so they are not mechanically interchangeable without changing the mounting position.