The Siemens 3VA9908-0BB24 is an undervoltage release accessory for the SENTRON 3VA molded-case breaker family — specifically the 3VA1 and 3VA20 through 3VA25 frames. It drops the breaker when supply voltage falls below its dropout threshold, which is the standard way to implement undervoltage protection on a motor feeder or process line without a separate relay.
Rated 120-127 V AC 50/60 Hz, so it's sized for the common North American control-voltage tap off a 120 V control transformer. The 4 kV surge withstand (overvoltage category III) means it's designed for the main distribution panel environment, not just a sub-panel — pollution degree 3 confirms it tolerates conductive dust and humidity you'd find in an industrial enclosure. Maximum apparent power draw is 2 VA — negligible on the control transformer budget. The three wiring slots accept conductors stripped to 10 mm (0.4 in), which is standard for 1.5–2.5 mm² control wiring. Physical footprint: 28.8 mm deep, 25.7 mm wide, 65.1 mm tall. That's the same width as a single modular unit (about 1 inch), so it clips into the breaker's accessory slot without stealing extra DIN-rail space.
Deployment context
Snaps into the accessory slot on 3VA1 and 3VA20–3VA25 breakers — no separate DIN-rail mount or panel drilling needed. The release sits inside the breaker's own housing, so the overall panel depth doesn't change. Wiring runs from the control transformer secondary to the release's terminals; the breaker trips when the control voltage drops out, which is standard for undervoltage protection on conveyor drives, pump starters, and process interlocks.