What this part does in the panel
The Siemens 3RA1921-2F is a SIRIUS hybrid link module that provides the mechanical and electrical interconnection between a 3RV1.2 circuit breaker (size S0, screw-type terminals) and a 3RT1.1 contactor (size S00, spring-type terminals). It replaces the need for separate wiring between the breaker and contactor, saving panel space and reducing assembly time on a DIN-rail motor starter assembly.
Lifecycle reality — this is a phased-out part
The 3RA1921-2F is officially a phased-out product. The manufacturer lists the preferred successor as the SIRIUS 3RA2921-2F. If you are filling a BOM line or stocking spares for an existing panel design, the 3RA2921-2F is the drop-in replacement to specify going forward.
This module is designed for the 3RV1.2 screw-type circuit breaker (size S0) and the 3RT1.1 spring-type contactor (size S00). It physically bridges the two devices, aligning the breaker output terminals with the contactor input terminals. The contactor size is S00, meaning it handles motor loads up to about 7.5 kW at 400 V AC-3 (typical for a 3RT1.1 contactor in that frame). The circuit-breaker size is S0, which covers the upstream protection range for that contactor class.