What this breaker is for
The Siemens SENTRON 5SY4450-8FA is a 4-pole miniature circuit breaker (MCB) with a D tripping characteristic, rated 50 A at 400 V AC. The D-curve (10–20× In magnetic trip) is designed for loads with high inrush currents — motor starters, transformers, welding equipment, or groups of LED drivers. The 10 kA breaking capacity per EN 60898 at 400 V AC means it can safely interrupt a fault current up to that level without welding contacts or cascading upstream, which is the standard for most industrial distribution boards.
DIN-rail fit and terminal capacity
Mounts on a standard 35 mm DIN rail via the quick-assembly system — snaps on and off without tools. Occupies 4 width units (72 mm). Depth is 76 mm, height 90 mm, so it fits flush in a standard 100 mm deep enclosure with the gland plate intact. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — enough for a 50 A feed using 10 mm² or 16 mm² Cu. Screw terminals with 3.5 N·m tightening torque, combined top and bottom entry. Sealable cover for tamper-proofing after inspection.
Environmental and compliance
Rated IP20 with connected conductors — suitable for dry indoor panels. Operating ambient -25 to +55 °C; storage -40 to +75 °C. Halogen-free and silicon-free construction, important for clean-room or semiconductor-adjacent installations where outgassing contaminates optics or contacts.