The Siemens 3VA9988-0BA21 is a shunt trip (auxiliary release) accessory for the SENTRON 3VA family — specifically the 3VA10 up to 3VA14 and 3VA20 up to 3VA24 molded case circuit breakers. It fires the breaker open on a remote signal, which is what you need when an E-stop, safety relay, or PLC output needs to kill power without someone walking to the panel.
Coil pulls 670 VA at pickup — that's not a trivial inrush for a 24 VDC control transformer if you're running it through a small PLC relay output.
Physical footprint is compact: 65.1 mm tall, 21.7 mm wide, 31.2 mm deep. It snaps into the accessory slot on the breaker — no DIN rail space consumed beyond the breaker itself. Stripped length for the wiring is 10 mm (0.4 in), which is standard for the terminal type on these accessories.