What it is and where it fits
The Siemens 5SL4263-8 is a 2-pole miniature circuit breaker from the SENTRON 5SL series, rated 63 A at 400 V AC with a D tripping characteristic. The D-curve means it tolerates high inrush currents — typical for motor, transformer, or welding loads — without nuisance tripping, while still clearing faults at the rated 10 kA breaking capacity per EN 60898 and IEC 60947-2. It snaps onto a DIN rail and occupies 2 modular width units (36 mm), so it fits standard distribution boards and subpanels.
What the ratings mean for your panel
The 10 kA breaking capacity at 400 V AC (both per EN 60898 and IEC 60947-2) tells you this breaker can safely interrupt a fault current up to that level without welding its contacts or cascading damage upstream. That's standard for most commercial and light industrial sub-distribution. The D-curve trips magnetically between 10× and 20× In (630 A to 1260 A), so it's a deliberate choice for circuits with starting surges — a motor starting direct-on-line or a bank of discharge lamps. At 30 °C the breaker carries the full 63 A; at 40 °C it derates to 59.67 A, and at 55 °C to 54.29 A — you'll need to account for enclosure heat rise if the panel runs warm.
Integration notes
Mounts in any position on a DIN rail. Depth is 76 mm (installation depth 70 mm), height 90 mm, width 36 mm — two modular units. IP20 with connected conductors, so it's intended for enclosed distribution boards, not wet or dusty environments. The housing is halogen-free and silicon-free, which matters for panels in transit, marine, or clean-room applications where outgassing can cause contact corrosion. Sealable with a lead or tag to prevent unauthorized switching. Pollution degree 2, overvoltage category III — standard for fixed-installation sub-distribution.