The Siemens SENTRON 5SY8450-8BB08 is a 4-pole miniature circuit breaker with a D tripping characteristic, rated 50 A at 400 V AC. Its 20 kA breaking capacity per IEC 60947-2 means it can safely interrupt fault currents up to that level without upstream coordination failure — a figure that governs the SCCR headroom for the downstream panel. The D-curve (10–20× In magnetic trip) is sized for transformer inrush or motor starting loads where a B or C curve would nuisance trip on the magnetizing draw.
Mounts via quick assembly system to DIN rail — the 72 mm width occupies 4 width units. Any mounting position is permitted, and the installation depth is 70 mm (total depth 76 mm). Combined terminals top and bottom accept solid or stranded conductors from 0.75 to 35 mm², torqued to 2.5–3.5 N·m. The IP20 rating (with connected conductors) means it lives inside an enclosure, not on a wet panel face. Sealable, halogen-free, silicon-free — relevant for clean-room or pharmaceutical GMP lines where material outgassing triggers a deviation.
The 5SY8450-8BB08 is a 4-pole, 50 A D-curve unit. A common peer is the 5SY4140-7 — a 1-pole, 40 A B-curve MCB. The 5SY8450-8BB08 will not drop into a panel specified around the 5SY4140-7 without rewiring: different pole count, different width (4 units vs 1), different curve, and different terminal capacity. The 5SY8450-8BB08 is for a three-phase plus neutral circuit with a high-inrush load; the 5SY4140-7 is for a single-phase lighting or control circuit. No direct second-source relationship — they serve different protection profiles.
Overvoltage category III — rated for fixed-installation distribution panels, not just downstream equipment. Ambient operating range -25 to +45 °C; storage from -40 to +75 °C. The magnetic-only tripping design means no thermal bimetal — the D-curve is purely electromagnetic, so ambient temperature does not shift the trip threshold the way a thermal-magnetic breaker would. The 5 kA rating under UL 1077 and CSA C22.2 No.235 covers North American supplementary protection applications; the 20 kA per IEC 60947-2 governs the European main-distribution SCCR declaration.