The 6 kA breaking capacity at 400 V (typical for a 3-pole MCB in a 3-phase system) means this breaker can safely interrupt a fault current up to 6,000 A without welding its contacts or failing catastrophically — that's the standard rating for most commercial distribution boards. The B characteristic (instantaneous trip at 3–5× In, so 60–100 A for this 20 A unit) is sized for circuits with low inrush: lighting, socket outlets, control transformers. If your load includes motors or drives, you'd want a C or D curve to avoid nuisance trips on startup.
Deployment context
The 3-pole format occupies three modular units (17.5 mm per pole). Wire termination is via screw terminals accepting up to 25 mm² conductor — typical for a 20 A feed in a commercial installation.