What it is and what it does
The Siemens 5SY4450-7 is a SENTRON 4-pole miniature circuit breaker rated 50 A with a C tripping characteristic. It switches and protects final circuits in commercial and industrial panels — motor starters, lighting distribution, control transformers — where the inrush from inductive or capacitive loads would nuisance-trip a B-curve device. The C-curve trips magnetically at 5 to 10 times rated current, so it holds through the startup surge of a 50 A motor branch and clears a hard fault fast.
Breaking capacity and dual-standard rating
This breaker carries two interrupting ratings: 10 kA per EN 60898-1 and 15 kA per IEC 60947-2 / UL1077. The higher 15 kA figure applies when the part is specified as a circuit breaker for industrial control panels (IEC 60947-2); the 10 kA rating covers the same part used as a domestic-style MCB (EN 60898). For a 50 A 4-pole breaker on a 400 V supply with a transformer impedance of 4–5%, the prospective fault current at the panelboard typically lands between 6 and 12 kA — the 15 kA IEC rating gives headroom without stepping up to a larger frame.
Panel fit and environmental tolerance
Occupies 4 modular width units (72 mm) on a DIN rail, depth 76 mm, installation depth 70 mm. Mounts in any position. Sealed with a lockable cover (sealable: yes). Rated IP20 with conductors connected — fine inside a locked panel, not for washdown zones. Ambient range -40 °C to 75 °C, with a derating curve starting at 35 °C: 50 A at 35 °C, 48 A at 40 °C, 45.95 A at 50 °C, 43.8 A at 60 °C. Pollution degree 3, overvoltage category III. Halogen-free and silicon-free construction.