What the ratings mean for fit
The Siemens 5SY7250-6 is a 2-pole miniature circuit breaker from the SENTRON series, rated 50 A at 35 °C with a B tripping characteristic. The B curve means it trips at 3–5× rated current — standard for resistive and general-purpose loads where inrush is low, like lighting or control transformers. At 400 V AC, the interrupting capacity is 15 kA per EN 60898 and 20 kA per IEC 60947-2; the higher IEC figure applies when the breaker is used in industrial distribution where the prospective fault current is known to be higher. Pollution degree 3 and overvoltage category III suit it for permanent installation in main or sub-distribution panels where conductive contamination is controlled but not absent.
Thermal derating and real-world current
The 50 A rating holds at 35 °C. Above that, the thermal-magnetic trip element derates: 46.35 A at 45 °C, 45.1 A at 50 °C, 43.75 A at 55 °C, and 42.4 A at 60 °C. If the panel ambient runs at 50 °C, size the load at 45 A, not 50. The breaker is rated for 50/60 Hz AC only.
Mounting and integration
Snaps onto DIN rail via the quick-assembly system, occupies 2 modular width units (36 mm wide). Installation depth is 70 mm; overall depth is 76 mm. Mounting position is any, and the supply cord can enter from either top or bottom — the combined terminal design accepts both. IP20 with connected conductors, so it's for enclosed panels only, not washdown areas. Sealable for lockout/tagout. Halogen-free and silicon-free, which matters in clean-room or sensitive electronics environments.