The Siemens SIRIUS 3RV1912-1CP0 is an undervoltage release for motor circuit breakers (S00, S0, S2, S3 frames). It drops the breaker when the control voltage falls below the dropout threshold, preventing an automatic restart after a brownout. The coil is rated 230 V AC at 50 Hz and 240 V AC at 60 Hz, with a leading auxiliary contact block providing 2 normally-open contacts that change state ahead of the main contacts.
Snap-on mounting onto the breaker's DIN-rail base. The 18.5 mm width matches one modular unit on the rail, and the 68 mm depth keeps the release within the breaker's profile — no extra enclosure depth needed. Screw-type terminals for the auxiliary and control circuit accept solid or stranded wire. The 2 NO contacts are leading — they make before the breaker's main contacts close and break after, so the control system sees the undervoltage state before the load re-energizes.