Siemens 5SL3125-7 SENTRON MCB — 25 A, 1-Pole, C-Curve
The Siemens 5SL3125-7 is a 1-pole miniature circuit breaker from the SENTRON range, rated 25 A at 400 V AC with a C tripping characteristic. It breaks 4.5 kA per EN 60898 and 5 kA per IEC 60947-2, covering residential and light commercial infrastructure branch circuits. The C-curve (5–10× In) suits moderate inrush loads like small motor starters, lighting banks, and transformer primaries where a B-curve would nuisance-trip on energization.
Thermal Derating & Ambient Rating
Full 25 A rating holds at 30 °C ambient. At 40 °C it derates to 23.48 A, at 45 °C to 22.5 A, and at 55 °C to 21 A. If the panel internal ambient runs above 40 °C — common in a packed enclosure near furnace controls or drive cabinets — the actual continuous current the breaker can carry drops by roughly 6% per 10 °C rise.
Physical Fit & Panel Integration
Occupies 1 modular unit (18 mm wide) on a DIN rail. Depth is 76 mm, installation depth 70 mm. Mounting position is unrestricted — horizontal, vertical, or inverted — which helps when laying out a dense sub-distribution board. IP20 with connected conductors; rated for pollution degree 2 and overvoltage category III, so it is intended for clean, dry indoor panels — not washdown or outdoor environments.
Compliance & Documentation
Halogen-free and silicon-free construction. Sealable terminals for tamper-proofing after commissioning. Mechanical service life rated at 10 000 switching cycles typical. Rated for both AC (400/440 V multi-phase, 250 V single-phase) and DC operation up to 72 V. DC rating is useful for control-circuit protection in the same panel.