The 5SY4204-8CC is a 2-pole SENTRON miniature circuit breaker rated 4 A with a D tripping characteristic, meaning it's built for loads with high inrush — motor starters, small transformers, or solenoid banks — where the magnetic trip needs to ride through the start surge without nuisance tripping. The 10 kA breaking capacity per EN 60898 tells you it can safely interrupt a fault up to that level at 440 V AC, which covers most industrial panel secondary circuits. At 40 °C ambient the continuous rating derates to 3.76 A, so if your panel runs hot, factor that in at the BOM stage.
Snaps onto DIN rail via the quick assembly system — 2 modular width units (36 mm wide), 76 mm deep, 90 mm tall. Mounts in any position, which helps when you're squeezing it into a crowded gland plate. IP20 with connected conductors is standard for enclosed panel gear.