The Siemens 3RV1921-1MA00-0FJ0 is an alarm switch designed for use with circuit-breaker sizes S0 through S3 from the Benedikt & Jaeger range. It signals the tripped or switched state of the breaker, giving the panel a remote indication without running separate sense wires into the breaker enclosure.
Mounts directly onto the S0, S1, S2, or S3 frame of the circuit breaker — no additional bracket or adapter needed. The switch mechanism engages with the breaker's internal trip indicator, so wiring it into the control circuit gives the PLC or annunciator a clean dry-contact signal on fault.