What it is and what it does
The Siemens 5SY8263-7 is a 2-pole miniature circuit breaker from the SENTRON family, rated 63 A at AC with a C-curve trip characteristic. It breaks faults up to 25 kA per IEC 60947-2, so it handles high-fault-current panels without blowing upstream — that's the number that decides whether it coordinates with your main breaker or not. On DC circuits it's rated 15 kA at 72 V max — good for control-power or battery-backed buswork, not for high-voltage DC strings. Single-phase or multi-phase operation tops out at 440 V AC, 50/60 Hz. That covers standard 400 V line-to-line industrial supplies across Europe and most of Asia.
Panel fit and derating
It's 36 mm wide — two modular units on a DIN rail. Depth is 76 mm, installation depth 70 mm. Mount in any position, quick-assembly system snaps onto the rail without tools. Rated 63 A at 45 °C ambient; at 50 °C it derates to 61.05 A, at 55 °C to 59.03 A. If your panel runs hot — say near a drive cabinet or in a non-climate-controlled enclosure — factor that derate into your load calculation. The breaker itself tolerates -40 to 75 °C ambient, so the enclosure temp, not the breaker, is your limit. IP20 with conductors connected — fine inside a panel, not for washdown or outdoor exposure without an enclosure.