What it is and what the ratings mean
The Siemens 5SY7263-7CC is a SENTRON miniature circuit breaker (MCB) — 2 poles, C-characteristic, rated 63 A at AC. The C-curve trips between 5 and 10 times rated current, so it handles moderate inrush from motor starters and small transformers without nuisance opening, while still clearing a hard fault fast. The 20 kA breaking capacity under IEC 60947-2 means it can safely interrupt a short-circuit fault up to 20,000 A at the supply side — adequate for most industrial panelboards fed from a transformer of 630 kVA or less. Under UL 1077 and CSA C22.2 No. 235 the interrupting rating is 5 kA, so verify the available fault current at the point of installation if the panel carries a North American listing.
Thermal derating — the real-world current limit
The 63 A rating holds only at 35 °C ambient. At 40 °C the breaker must be derated to 59.54 A; at 45 °C to 57.71 A; at 50 °C to 55.82 A; at 55 °C to 53.86 A. If the panel ambient runs above 35 °C — common in a sealed enclosure with other heat sources — size the upstream conductor and load for the derated figure, not the nameplate 63 A. The breaker can be mounted in any position, which helps airflow management in a crowded DIN rail.
Panel integration and mounting
Two modular width units (36 mm wide) on a DIN rail. Depth is 76 mm, installation depth 70 mm. The quick-assembly fastening system clips onto the rail without tools. Both top and bottom terminals accept combined (screw + clamp) conductors. IP20 with conductors connected — standard for enclosed distribution boards; not rated for wet or dusty environments. The breaker is sealable, halogen-free, and silicon-free, which keeps it compliant for clean-room or food-grade panels where outgassing matters.