The Siemens 3VA9978-0BB12 is a SENTRON undervoltage release — an auxiliary accessory that trips a 3VA4, 3VA5, or 3VA6 molded-case circuit breaker when its 48 V DC control voltage drops below the dropout threshold. It's a panel-mount add-on that snaps into the breaker's accessory slots, not a standalone device. The release draws a maximum of 2.5 W from the DC control circuit at steady state. That's the coil holding power once the breaker is closed; the momentary pickup surge is higher but brief.
Dimensions are 25.7 mm wide, 65.1 mm high, and 28.8 mm deep — it's a compact module that fits inside the breaker's accessory bay. The 3-slot design means it occupies one of the three available positions in the 3VA frame. Wire stripping length is 10 mm (0.4 in) for the AWG 18 / 750 mm connection. That's standard for spring-cage or screw terminals on this class of auxiliary; strip to that length and no more to avoid exposed conductor outside the clamp.