What this 1 A D-curve MCB is for
The Siemens 5SL4301-8CC is a 3-pole miniature circuit breaker from the SENTRON 5SL family, rated 1 A with a D tripping characteristic and a 10 kA breaking capacity per EN 60898 at 400 V AC. The 3-pole construction switches all three phases simultaneously, so it fits three-phase sub-circuits in residential or light infrastructure panels.
Snaps onto standard DIN rail — 3 width units (54 mm wide) — and accepts conductors from 0.75 mm² up to 25 mm², which covers both control wiring and power feed-through in a distribution board.
The D-curve's magnetic trip threshold (10–20× In) means it holds through the inrush of a small control transformer or a 0.25 kW motor starting direct-on-line, but still clears a hard short. Rated frequency is 50 Hz; maximum multi-phase voltage is 440 V AC.