Breaking capacity and dual-standard rating
The 5SY4301-8: This MCB carries two breaking-capacity ratings: 10 kA under EN 60898-1 and 35 kA under IEC 60947-2 / UL1077. The higher 35 kA figure applies when the breaker is used as a supplementary protector per 60947-2 — important for panel builders who need to coordinate with upstream fault levels above 10 kA.
Temperature derating and panel placement
The 5SY4301-8 is rated 1 A at 35 °C, but derates to 0.95 A at 40 °C, 0.93 A at 45 °C, 0.9 A at 50 °C, 0.88 A at 55 °C, and 0.85 A at 60 °C. In a crowded DIN-rail enclosure with multiple breakers side by side, ambient temperature near the breaker can rise 10–15 °C above the room — factor the derated current into the load calculation, not the 35 °C figure. Mounts in any position, and the quick-assembly system snaps onto the rail without tools.