The Siemens 3RV1912-1CV1 is a SIRIUS undervoltage release designed to drop a 3RV10 motor circuit breaker when the control voltage falls below its holding threshold. It carries 2 NO leading auxiliary contacts that change state ahead of the main breaker contacts, giving the PLC or safety relay a status signal before the power circuit opens. That leading-contact timing matters when you need to sequence a downstream drive stop or confirm the drop-out before a restart. At 18.5 mm wide and 68 mm deep, it tucks into the same rail footprint as the breaker it serves — no extra panel real estate needed.
Breaker compatibility and panel fit
Listed for 3RV10 circuit breakers in frame sizes S00, S0, S2, and S3. It clips onto the left side of the breaker without tools. The 18.5 mm width matches the accessory slot on those breakers — it does not add a full module width to the rail. Depth of 68 mm is shallower than the breaker body (75 mm on S00 frames), so it stays inside the gland-plate clearance envelope. Rated insulation voltage 690 V AC, pollution degree 3. Front face is IP20 finger-safe — acceptable for open-panel installation.
If your control transformer taps 400 V at 50 Hz, the release still holds in — the dropout threshold is a percentage of rated voltage, typically 70–35 % of Ue. At 400 V the coil sees about 96 % of its 415 V rating, well above the dropout zone.