What it is and what it does
The Siemens 3RV1902-1AB4 is a SIRIUS undervoltage release — a control accessory that trips a motor circuit breaker when its supply voltage drops below the dropout threshold. It is designed for use with Siemens SIRIUS 3RV1 and 3RV2 circuit breakers in frame sizes S00, S0, S2, and S3. The release is rated 24 V DC control voltage and snaps onto the breaker's side via the standard DIN-rail-compatible snap-on mounting, so it integrates directly into a panel without extra brackets or wiring channels.
Key ratings and what they mean for fit
The 24 V DC control supply means this release is intended for low-voltage DC control circuits — common in PLC-driven panels where 24 V DC is the standard control voltage. The 690 V rated insulation voltage (degree of pollution 3) tells you it is safe to install in a motor starter panel where the main circuit operates at up to 690 V AC, a typical industrial supply in many regions. The IP20 front protection with finger-safe touch protection per IEC 60529 means the front of the release is safe for operators to be near; the panel itself still needs an enclosure for the live terminals.
Mounting and panel integration
Snap-on mounting onto the side of the circuit breaker — no tools needed, no DIN-rail slot consumed. The release measures 68 mm deep, 18.5 mm wide, and 90 mm high. The narrow width (18.5 mm) means it adds minimal footprint to the breaker assembly, which matters when you are packing multiple motor starters into a control cabinet. The operating temperature range is -20 to +60 °C, storage -50 to +80 °C, covering most indoor industrial environments.