What this 63 A B-curve MCB does in a panel
The Siemens SENTRON 5SY7663-6 is a 4-pole miniature circuit breaker (3P+N) rated 63 A at 35 °C with a B tripping characteristic — meaning it trips between 3 and 5 times rated current, fast enough for residential and light commercial cable protection but without the nuisance trips a C-curve might cause on motor inrush.
Derating and temperature — the real-world current limit
The 63 A rating holds at 35 °C ambient. At 40 °C it derates to 59.98 A, at 45 °C to 58.4 A, at 50 °C to 56.83 A, at 55 °C to 55.12 A, and at 60 °C to 53.42 A.
The 5SY7663-6 occupies 4 modular width units (72 mm) with a depth of 76 mm and installation depth of 70 mm. The B-curve characteristic is energy limitation class 3, meaning it limits let-through energy on short circuits.