The Siemens 5SY6250-6 is a 2-pole miniature circuit breaker from the SENTRON family, rated 50 A at 35 °C with a B tripping characteristic (instantaneous trip between 3 and 5 times rated current). The B-curve means it clears short-circuit faults fast enough to protect cable runs and resistive loads, but it will nuisance-trip on moderate inrush from motor or transformer loads — this is the curve to pick for general-purpose lighting, distribution, and control circuits, not for heavy inductive starts.
Breaking capacity and what it means for coordination
Thermal derating and ambient range
The 50 A rating is at 35 °C ambient. At 40 °C it derates to 47.6 A, at 50 °C to 45.1 A, and at 55 °C to 43.75 A. Operating ambient range spans -40 °C to 75 °C, with humidity limits of 95% up to 55 °C, 55% up to 70 °C, and 35% at 75 °C. The -40 °C floor covers cold storage or unheated outdoor enclosures; the 75 °C ceiling is above typical panel ambient but allows for localized hot spots near the breaker.
The part is halogen-free and silicon-free, which simplifies compliance documentation for RoHS and REACH declarations.