The Siemens 5SJ6503-7 is a 1P+N SENTRON miniature circuit breaker with C-curve tripping, rated 3 A at 240 V AC and breaking 6 kA per EN 60898 (also 6 kA per IEC 60947-2). At 3 A it's sized for small branch circuits: lighting strings, control transformers, or single-phase motor feeds under 0.75 kW. The 1P+N design switches the phase and disconnects the neutral — the neutral is not switched under load but is disconnected when the breaker is in the off position, which matters for isolation requirements in some national wiring rules. Mounting position is any, installation depth 70 mm, so it fits the same 18 mm pitch DIN-rail enclosures as the rest of the 5SJ6 family.
The 70 mm installation depth keeps it flush with other SENTRON 5SJ6 devices in a distribution board. The terminal accepts solid conductors from 0.75 to 25 mm² and stranded from 0.75 to 25 mm², which covers everything from 1.5 mm² lighting tails up to 6 mm² submains. Sealable per the spec, so you can lock the toggle with a seal wire for tamper-proof isolation on shared panels.