The Siemens 3RV1901-1EA00-0FJ0 is an auxiliary switch with one normally open and one normally closed contact, designed for transverse mounting on circuit-breakers in the S00 through S3 frame sizes. It signals the breaker's open/closed state back to a control system — a common need on MCC buckets or standalone motor starter enclosures where you need a feedback contact for a PLC input or a status lamp.
Integration Note
Mounts transversely on the side of a circuit-breaker in frame sizes S00, S0, S1, S2, or S3. The 1NO+1NC contact arrangement gives one make and one break signal.