The Siemens SENTRON 5SJ6363-6 is a 3-pole miniature circuit breaker with a B tripping characteristic, rated 63 A at 400 V AC and a 6 kA breaking capacity.
The 6 kA breaking capacity (both EN 60898 and IEC 60947-2) tells you it can safely interrupt a fault current up to 6,000 A without welding its contacts or failing catastrophically. In a typical 400 V three-phase distribution board, that's enough for most downstream faults unless you're feeding a transformer with a high short-circuit capacity upstream. The B characteristic (3-5x In) means it holds through brief surges like a capacitor bank charging but trips fast on a hard short — good for circuits where you want selectivity with upstream C-curve breakers.
Terminals accept solid or stranded conductors from 0.75 mm² up to 25 mm² — that's enough for a 63 A feed using 10 mm² or 16 mm² copper, depending on your local code and derating. The terminals are sealable (a lead seal wire can be threaded through to prevent tampering after commissioning). Mounting position is any — horizontal, vertical, upside down — no derating required for orientation.