What this shunt trip does on the line
The Siemens SENTRON 3VA9988-0BA22 is a shunt trip accessory — an auxiliary release that remotely trips a 3VA molded-case breaker when you apply 110-127 V AC at 50/60 Hz. It's designed for the 3VA10 through 3VA14 and 3VA20 through 3VA24 frames, so if you're retrofitting an existing SENTRON panel or building a new one, this is the part that lets an emergency-stop button, a safety relay, or a PLC output kill the breaker without an operator pulling the handle. Rated for 810 VA apparent power at maximum draw, it's not a low-energy signal coil — the inrush will pull some current, so size your control transformer accordingly.
The accessory occupies three slots on the breaker, so it will add width to the assembly. The body dimensions are 31.2 mm deep, 21.7 mm wide, and 65.1 mm tall — that depth is the dimension that matters when you're sliding it into a panel with a shallow backpan or a rear-mounted bus. The stripped length for the terminals is 10 mm (0.4 in), which is standard for this class of accessory; strip to that length and no more, or you risk exposed conductor past the cage.