The Siemens 3VM9908-0BB10 is a SENTRON undervoltage release — an auxiliary release accessory designed for the 3VM series of molded-case circuit breakers up to 630 A. It trips the breaker when its 12 V DC control supply drops below the dropout threshold, providing undervoltage protection for downstream loads.
The 3VM9908-0BB10 snaps into the accessory slot of the 3VM breaker frame. Its dimensions — 65.1 mm height, 25.7 mm width, 28.8 mm depth — keep it within the breaker's existing envelope; no additional DIN-rail space is consumed. The stripped length for wiring is 10 mm (0.4 in).