What the ratings mean for fit
The Siemens SENTRON 5SL4125-6 is a 1-pole miniature circuit breaker with a B-tripping characteristic, rated 25 A at 30 °C and 400 V AC. The 10 kA breaking capacity (per EN 60898 and IEC 60947-2) means it can safely interrupt short-circuit faults up to 10 kA without upstream damage — sized for residential and light commercial distribution boards where the prospective fault current stays under that threshold. The B-curve (3–5× In instantaneous trip) protects cable runs and resistive loads; it is not intended for motor-starting inrush, which needs a C or D curve. Temperature derating is published: 23.1 A at 40 °C, 22 A at 45 °C, 19.91 A at 55 °C — factor that into the continuous load if the panel runs warm.
Panel integration and environment
Snap-on DIN rail mount, 18 mm width (1 modular unit), 76 mm depth, 70 mm installation depth. Any mounting position is allowed. IP20 with conductors connected — fine for enclosed distribution boards; not rated for wet or dust-exposed locations. Pollution degree 2, overvoltage category III. Sealable, halogen-free, silicon-free. Accepts supplementary devices (auxiliary switches, shunt trips, alarm contacts) on the right side. Power loss is 3 W per pole at rated current in hot state.