The Siemens 3VA9988-0BM10 is a SENTRON shunt trip auxiliary release designed for left-side mounting on 3VA1 and 3VA20 through 3VA25 molded-case circuit breakers. It operates on 24 V DC and provides remote tripping for electrical interlocking schemes — common in transfer-switch or emergency-off circuits where one breaker must force the other open before closing.
Snaps into the left accessory slot of the 3VA breaker frame. The release occupies a 25.7 mm width (roughly 1.5 modular units) and extends 31.2 mm from the breaker body; height is 65.1 mm, matching the breaker profile so it doesn't overhang the DIN rail. Strip 10 mm (0.4 in) of insulation on the control wires for the spring-cage terminals — the three connection slots accommodate the two coil wires plus a common return if daisy-chaining multiple releases.
The 24 V DC coil is standard for control circuits in panel builds; verify polarity on the spring-cage terminals before energizing.