What this MCB does in the panel
The Siemens SENTRON 5SJ4163-6HG40 is a 1-pole miniature circuit breaker with a B tripping curve, rated 63 A at AC and 60 V DC maximum. It mounts on a standard DIN rail, occupies one modular width (18 mm), and is rated for overvoltage category III with pollution degree 3. The B curve means it trips between 3 and 5 times rated current — suited for resistive or general-purpose loads where inrush is moderate, not for motor-heavy circuits that need a C or D curve.
Thermal derating — the real ampacity
The 63 A rating holds at 30 °C and 40 °C ambient. At 45 °C it derates to 61.1 A, at 50 °C to 59.9 A, at 55 °C to 58.3 A, and at 60 °C to 56.7 A. If the panel ambient runs above 40 °C, the continuous load must be reduced accordingly — the 63 A label is not the limit in a hot enclosure.