What this MCB is and what the ratings mean
The Siemens 5SL7220-3RC is a 2-pole miniature circuit breaker rated 20 A with a K-trip characteristic and a 15 kA breaking capacity. The K curve means it holds through short-duration inrush up to 8–12× rated current — sized for motor, transformer, and inductive loads where a B or C curve would nuisance-trip on startup. The 15 kA interrupting rating at 400 V tells you it can clear a hard fault up to that level without welding contacts or cascading upstream; that is the figure the panel designer uses for SCCR coordination. It is a current-production part, so the BOM line is stable for new builds and replacements alike.
Deployment context
Snap-on DIN-rail mounting for 35 mm rail per EN 60715. Two-pole width (36 mm) occupies two module spaces in the distribution board. Rated for 50/60 Hz networks — standard for commercial and light industrial panel builds.