Siemens 5SL6125-6MB — SENTRON 1-pole B-curve MCB, 25 A, 6 kA
The Siemens 5SL6125-6MB is a SENTRON miniature circuit breaker, 1-pole, with a B tripping characteristic, rated 25 A at 30 °C and 230/400 V AC. Its 6 kA breaking capacity per EN 60898 covers most residential and light commercial branch circuits — think lighting, socket outlets, and general-purpose loads where inrush is modest. The B-curve trips between 3 and 5 times rated current, so it's a good fit for resistive and small inductive loads, but not for motor starts or transformer inrush where a C or D curve would be needed. At 18 mm wide (1 modular unit), it snaps onto standard DIN rail and occupies one slot in a distribution board. Depth is 76 mm, installation depth 70 mm — check your enclosure depth if you're retrofitting into a shallow panel. Rated for overvoltage category III and pollution degree 2, which is standard for fixed-installation downstream of the utility meter.
What the ratings mean for fit
The 25 A rating at 30 °C is the continuous current the breaker carries without tripping in a 30 °C ambient. If your panel runs hotter, you'll need to derate — the 25 A figure at 30 °C is the baseline. The 6 kA breaking capacity per EN 60898 means it can safely interrupt a fault current up to 6 kA at 230/400 V AC. That's adequate for most residential and light commercial service entrances where the prospective short-circuit current is under 6 kA. If your installation has a higher fault level (e.g., near a large transformer), you'd need a breaker with a higher breaking capacity, like the 10 kA or 15 kA variants in the 5SL series. The B-curve (3-5× In) is the standard choice for general-purpose circuits with resistive or small inductive loads. It's not intended for motor circuits or high-inrush loads — those would need a C or D curve to avoid nuisance tripping on startup. The 1-pole design switches the line conductor only; neutral is not switched. For single-phase circuits, the rated voltage is 250 V AC; for multi-phase (e.g., 2- or 3-pole ganged) it's 440 V AC maximum.
Mechanical and environmental
Rated for 10,000 mechanical switching cycles typical. Ambient temperature range -40 °C to 75 °C, which covers most indoor and sheltered outdoor installations. IP20 with connected conductors — not suitable for wet or dusty environments without additional enclosure. Halogen-free and silicon-free, which matters for installations in sensitive environments like hospitals or data centers where off-gassing from a fault could damage equipment.