What this MCB does on the rail
The Siemens SENTRON 5SL6125-6 is a 1-pole miniature circuit breaker with a B tripping characteristic, rated 25 A at 30 °C and 400 V AC per EN 60898. Its 6 kA breaking capacity covers residential and light commercial distribution boards where the prospective short-circuit current stays under that threshold. The B curve means it trips between 3 and 5 times rated current — typical for resistive and general-purpose loads where inrush is modest. At 40 °C ambient the continuous rating drops to 23.48 A; at 55 °C it's 21 A, so derate if the panel runs hot. Single-pole format occupies one modular width (18 mm) on a DIN rail, and the IP20 rating with connected conductors is standard for enclosed distribution boards.
Physical fit and environment
Width 18 mm (one modular unit), depth 76 mm, height 90 mm — fits any standard 35 mm DIN-rail enclosure. Installation depth 70 mm leaves clearance for rear busbars. Mounting position any orientation; pollution degree 2 (non-conductive, occasional condensation). Temperature range -40 °C to 75 °C covers unheated utility rooms and outdoor-adjacent cabinets. Halogen-free and silicon-free construction matters for clean-room or high-reliability environments where outgassing can't be tolerated. Sealable terminals allow lockout/tagout compliance. Supplementary devices (auxiliary contacts, shunt trips, alarm switches) can be snapped on the right side.
Electrical ratings and coordination
Rated 25 A at 230/400 V AC, single-pole switching. Breaking capacity 6 kA per both EN 60898 and IEC 60947-2 — that's the same standard for residential and industrial coordination. Overvoltage category III (distribution level). Energy limitation class 3 means it limits let-through energy for downstream equipment protection. Mechanical endurance 10 000 operating cycles typical. Power loss 2.8 W per pole at rated current in hot state — factor into thermal calculations for multi-pole assemblies in compact enclosures.