Siemens 5SY5125-6KK11 — 1P B-Curve MCB, 25 A, 10 kA, Railway-Rated
The Siemens 5SY5125-6KK11 is a 1-pole SENTRON miniature circuit breaker with a B-curve tripping characteristic, rated 25 A at 400 V AC and 10 kA breaking capacity per EN 60898. It also carries a DC rating of 220 V with 10 kA interrupting capacity per EN 60898-2, making it suitable for mixed AC/DC control circuits in a single enclosure. Rated for universal current operation (AC/DC), this breaker handles both power and control loads without derating the trip curve — a practical advantage when the same rail feeds a 24 VDC relay bank and a 230 VAC contactor coil.
The 25 A B-curve trips between 3× and 5× rated current (75–125 A magnetic release), so it protects lighting, control transformers, and general-purpose circuits where inrush is moderate. Energy limiting class 3 means the breaker clears a fault fast enough to limit let-through energy, reducing thermal stress on downstream wiring and connected equipment. This is one of the highest energy-limiting classes per IEC standards. The 18 mm width (1 width unit) fits standard DIN-rail enclosures.
The quick-assembly mounting system clips onto standard DIN rail without tools.