What it is and what it does
The Siemens 5SY7205-7 is a 2-pole miniature circuit breaker from the SENTRON family, designed for branch-circuit protection in industrial control panels and distribution boards. Its C-curve tripping characteristic means it handles moderate inrush currents — typical for motor starters, contactor coils, and small transformers — without nuisance tripping, while still clearing overloads and short circuits. Rated 400 V AC, it carries a 15 kA breaking capacity per EN 60898 and a 50 kA rating per IEC 60947-2, so it can safely interrupt high-fault currents on a 400 V line. The 2-pole design switches both phase conductors; there is no neutral switching. It snaps onto a DIN rail via the quick assembly system and occupies 2 modular width units (36 mm,).
What the ratings mean for fit
The 15 kA breaking capacity at 400 V AC per EN 60898 is the rating that governs most commercial and light-industrial installations — it tells you the breaker can clear a fault up to that level without welding its contacts or rupturing the case. The 50 kA rating per IEC 60947-2 applies when the breaker is used in an industrial context where the prospective short-circuit current is higher; that figure matches the requirements of a main distribution board fed by a large transformer. For DC circuits, the same 15 kA rating applies per IEC 60947-2. Under UL 1077 and CSA C22.2 No. 235, the interrupting capacity is 5 kA — this matters if the panel is destined for a North American job that requires UL listing. The C-curve trips magnetically between 5 and 10 times rated current, so it holds through the starting surge of a small motor or a bank of contactors. Pollution degree 3 and overvoltage category III confirm it is rated for fixed installations inside an enclosure where conductive pollution is possible — typical for a factory-floor panel. The IP20 rating means it is protected against solid objects larger than 12 mm (fingers) but not against moisture; it must live inside a sealed cabinet.
Panel integration details
Mounts in any position on a DIN rail; the quick assembly system clips it on without tools. Depth is 76 mm, installation depth 70 mm — the extra 6 mm accounts for the front handle and terminal screws. Width is 36 mm, which is 2 modular units, so it occupies two 18 mm slots on the rail. Combined terminals top and bottom accept copper conductors; the sealable feature lets you lock the handle in the OFF position with a padlock for lockout/tagout. Vibration resistance per IEC 60068-2-6: ±1 mm at 5 to 25 Hz, 50 m/s² at 25 to 150 Hz — it holds up on a machine frame or a panel door subject to moderate vibration. Mechanical service life is 10 000 operating cycles typical.