The Siemens 3RV2901-2C is a SIRIUS lateral auxiliary switch designed to snap onto the side of 3RV2 circuit breakers in sizes S00, S0, S2, and S3. It provides two normally-closed (NC) instantaneous contacts via spring-loaded terminals — no screw torque to verify, no vibration loosening over time. The 9.5 mm width and 68 mm depth keep the assembly within the breaker's own envelope, so the DIN-rail footprint doesn't grow.
The auxiliary contacts carry a maximum AC-12 rating of 10 A — that's the resistive-load limit for signaling or pilot-duty circuits. For inductive loads typical of contactor coils or relay solenoids (AC-15 duty), the rating drops to 1 A at 690 V. Per the datasheet, the switch handles 3 A at 400 V and 10 A at 690 V, but those figures apply under specific utilization categories; the AC-15 number is the one to size against when switching magnetic loads. At 24 V the contact rating is 2 A, at 110 V it's 0.5 A, and at 230 V it's 4 A — so the same switch covers both control-voltage levels common in North American and European panels.
Spring-loaded terminals accept solid or stranded conductors from 0.5 to 2.5 mm² (2x 0.5...2.5 mm² per clamp), or 2x 20–14 AWG. No screwdriver calibration needed — strip to 8–10 mm, push the spring, insert, release. The plug-in fixing method means the switch clips onto the breaker side without tools; removal requires a small flat-blade to release the latch.