Siemens 5SY8263-8 — 63 A D-Curve MCB for High-Inrush Loads
The Siemens 5SY8263-8 is a 2-pole SENTRON miniature circuit breaker rated 63 A with a D tripping characteristic, designed to handle the high inrush currents of motor starters, transformers, and welding equipment without nuisance tripping. Its 20 kA breaking capacity at 400 V AC per IEC 60947-2 means it can safely interrupt fault currents up to that level in industrial panel applications, providing adequate SCCR headroom for most distribution boards. The 15 kA DC rating per IEC 60947-2 covers DC-side protection in rectifier-fed circuits. Rated 63 A at 45 °C ambient, it derates to 61.05 A at 50 °C and 59.03 A at 55 °C — a thermal curve worth checking if the breaker sits in a warm enclosure alongside other heat-generating devices. The 2-module-width (36 mm) footprint snaps onto DIN rail in any mounting position, with combined top and bottom terminals that accept incoming feed from either direction.
Panel Fit & Environment
The 36 mm width (2 modular units) and 76 mm depth fit standard DIN-rail enclosures; the 70 mm installation depth leaves clearance behind the rail for wiring. IP20 with connected conductors means it is protected against finger contact but not washdown — suitable for indoor control panels, not wet areas. The -40 to 75 °C operating range covers unheated warehouses and roof-mounted cabinets. Halogen-free and silicon-free construction matters for environments sensitive to outgassing, such as clean rooms or sealed enclosures near sensitive electronics.