Siemens 5SY7125-6 SENTRON MCB — 1-pole, 25 A, B-curve, 15/25 kA
The Siemens 5SY7125-6 is a 1-pole miniature circuit breaker from the SENTRON family, rated 25 A at 35 °C with a B tripping characteristic. It is designed for AC circuits up to 400 V at 50/60 Hz, and carries a breaking capacity of 15 kA per EN 60898 and 25 kA per IEC 60947-2. The 18 mm width (1 modular unit) snaps onto a DIN rail in any mounting position, making it a direct fit for standard distribution boards and subpanels.
What the ratings mean for fit
The B-curve (tripping characteristic class B) means the magnetic trip operates at 3 to 5 times rated current — suited for resistive or lighting loads with low inrush, not motor or transformer circuits. At 35 °C the continuous rating is 25 A; it derates to 22.68 A at 45 °C, 21.85 A at 50 °C, 21 A at 55 °C, and 20.1 A at 60 °C. The 15 kA breaking capacity per EN 60898 covers most residential and commercial service-entrance fault levels; the 25 kA rating per IEC 60947-2 gives headroom for industrial panel coordination studies where the prospective short-circuit current is higher.
Integration and compliance notes
Mounts on a DIN rail via the quick assembly system; the 18 mm width occupies one modular unit. The housing is IP20 with connected conductors, rated for pollution degree 3 and overvoltage category III. The combined top and bottom terminals accept sealable covers, and the part is halogen-free and silicon-free. Ambient temperature range is -40 °C to 75 °C. The manufacturer designates it per IEC 81346-2 as function F.