What this 0.3 A C-curve MCB is for
The Siemens 5SL6114-7BB is a 1-pole SENTRON miniature circuit breaker rated 0.3 A at 400 V AC, with a C tripping characteristic and a 6 kA breaking capacity per EN 60898 and IEC 60947-2. That 0.3 A rating is unusually low — it is sized for protecting control transformers, signal circuits, or small lighting loads where a standard 1 A or higher breaker would not clear a fault before the downstream wiring overheats. The C-curve means it trips magnetically between 5 and 10 times rated current (1.5 to 3 A), so it rides through inrush from small contactor coils or incandescent lamps without nuisance tripping, but still clears a hard short fast enough to protect the 0.75 mm² minimum wire size this breaker accepts. Rated for residential and infrastructure use, it mounts on a standard 18 mm wide DIN-rail slot — one width unit — and can be sealed to prevent tampering.
The breaker occupies 18 mm width on a DIN rail, 90 mm tall, 76 mm deep. The screw terminals accept solid or stranded conductors from 0.75 mm² up to 25 mm², with a recommended tightening torque of 2.5 to 3 N·m.