The Siemens 3RV1921-1M is a SIRIUS signaling switch designed for circuit breaker sizes S0, S2, and S3.
Contact ratings
The auxiliary contacts are rated for 10 A maximum, with voltage-specific switching capacities: 2 A at 24 V, 0.5 A at 110 V, 0.25 A at 220 V, 4 A at 230 V, 3 A at 400 V, and 10 A at 690 V. At AC-15 duty at 690 V the rated operational current is 1 A. These numbers define the signal load it can break — useful for sizing the downstream input card or relay coil.
Mounts via plug-in fixing directly onto the front of the circuit breaker — no DIN rail footprint required. The screw-type terminals accept 2x (0.5 to 1.5 mm²) and 2x (0.75 to 2.5 mm²) solid or finely stranded wire with core end processing. Overall dimensions are 18 mm wide, 90 mm tall, and 68 mm deep, so it stays within the breaker's own envelope.