The Siemens 5SY4220-8CV is a 2-pole miniature circuit breaker with a D20 trip curve and a rated short-circuit breaking capacity (Icu) of 15 kA at 400 V AC. The D-curve means it tolerates higher inrush currents — typically for motor or transformer loads — before tripping magnetically, so it won't nuisance-trip on a pump start or a control transformer energizing.
Where it lives in the panel
Two-pole width means it occupies two module spaces (36 mm on a standard 18 mm/module rail). The D20 rating makes it a common choice for motor feeder circuits or inductive loads where the starting surge exceeds what a C-curve would pass.