The Siemens 3VU2912-4AP0 is an undervoltage release designed for the 3VU2 series of motor protection circuit breakers. It operates on a 220/250V AC control supply and is compatible with the 3VU2.1, 3VU2.2, and 3VU2.3 breaker frames.
This is standard undervoltage protection: if the supply dips or fails, the release opens the breaker, preventing automatic reclosure when power returns. For a 3VU2 motor protection breaker, this release mounts directly onto the breaker body and shares its DIN-rail footprint in the panel.