The Siemens SIRIUS 3RV1982-1AA0 is an undervoltage release designed for the 3RV1.6, 3RV1.7, and 3RV1.8 series of motor starter protectors.
This undervoltage release snaps onto the side of the 3RV1 circuit breaker, occupying no additional DIN rail space. The 24–30 V AC/DC control coil is wired in series with the emergency-stop or undervoltage monitoring circuit — when the control voltage disappears, the release mechanically forces the breaker to trip. Verify the coil voltage matches your control transformer tap before wiring.