What this accessory does
The Siemens 3VA9978-0BL30 is a SENTRON shunt trip (auxiliary release) designed to remotely trip a 3VA4, 3VA5, or 3VA6 molded-case circuit breaker on command. It mounts in one of the three accessory slots on the breaker's right side. The coil accepts 24 V AC at 50/60 Hz or 24–30 V DC, drawing 30 VA apparent power on AC or 45 W on DC. That draw matters for control-transformer sizing and DC-supply budgeting, especially if multiple shunt trips share one supply.
Physical fit in the panel
The shunt trip body measures 25.7 mm wide, 65.1 mm high, and 31.2 mm deep. Width corresponds to roughly 1.5 modular DIN-rail units — plan the gland-plate fill accordingly if it sits next to other 18 mm-wide modules. Strip the control wires to 10 mm (0.4 in) for the screw terminals. That's a standard length for cage-clamp or screw-clamp terminations on SENTRON accessories.