What it is and what it does
The Siemens 3RV1902-1AV00-0FQ0 is an undervoltage release for SIRIUS 3RV circuit-breakers. It trips the breaker when supply voltage drops below the release threshold, protecting downstream loads from undervoltage conditions — a common requirement on motor circuits and conveyor drives where a restart after a sag could cause mechanical damage or unsafe restart. Rated for 400V AC at 50Hz, it mounts directly onto the breaker body, size S00 up through S3.