What this 63 A D-curve MCB is for
The Siemens SENTRON 5SJ4263-8HG41 is a 2-pole miniature circuit breaker with a D tripping characteristic, rated 63 A at both 30 °C and 40 °C ambient.
Thermal derating and real-world loading
The 63 A rating holds up to 40 °C ambient. Above that, the breaker derates linearly: 61.7 A at 45 °C, 60.4 A at 50 °C, 59.1 A at 55 °C, and 58 A at 60 °C. The breaker itself survives up to 75 °C ambient and down to -40 °C, but the continuous current capability shrinks above 40 °C.
Halogen-free and silicon-free construction — important for sensitive environments like clean rooms or semiconductor fabs where outgassing can contaminate processes. IP20 with connected conductors; IP40 in the handle range.