It's the part that makes a motor starter fail-safe on a power dip or emergency-stop string — the coil holds at 24 V DC nominal, and when that supply goes, the release mechanically opens the breaker within 20 ms. The 20 ms break time means the motor sees a clean disconnect before a partial-voltage stall can draw locked-rotor current.
Snap-on DIN integration for 3RV2 frame sizes
Mounts via snap-on fastening directly onto the side of a 3RV2 motor circuit protector — no tools, no DIN rail adapter. It fits the S00, S0, S2, and S3 frame sizes, so one accessory covers the whole 3RV2 family from the smallest 0.1 A protector up to the 100 A class. The 19 mm width adds exactly one modular unit to the breaker's footprint. In a crowded panel that's the difference between fitting a second starter row or needing a wider enclosure. Screw-type terminals on the control circuit accept standard ferrule-ended wire; strip length follows the 3RV2 terminal spec.
Lifecycle and compliance — active, RoHS, no LTB pressure
This is a current-production Siemens accessory, so the supply chain is stable. For a panel builder wiring a 3RV2-based motor starter group, the 3RV2902-1AB4 is the specified undervoltage release — no substitution needed.