The Siemens 5SJ6303-7 is a SENTRON 5SJ6 miniature circuit breaker, 3-pole, C-curve, rated 3 A at 400 V AC. The C-curve trips between 5 and 10 times rated current — 15 to 30 A — so it handles moderate inrush from motor starters or transformer banks without nuisance trips, while still clearing a hard fault. The 6 kA breaking capacity (per EN 60898 and IEC 60947-2) means it can safely interrupt a fault current up to 6 kA at the panel; if the available fault current at the installation point exceeds that, you need an upstream current-limiting device or a higher-rated breaker. The 3 A rating suits small motor circuits, control transformers, or lighting sub-circuits where the load draws under 3 A continuous. Terminals accept solid or stranded conductors from 0.75 to 25 mm² — enough for the 3 A load wiring plus any daisy-chained feed-through.
Mounts in any position on a DIN rail; installation depth is 70 mm, and the 3-pole body occupies 3 width units (roughly 54 mm). Ambient operating range is -20 to +45 °C, with storage from -40 to +75 °C. Vibration resistance tested to 50 m/s² at 25 to 150 Hz and 60 m/s² at 10 to 150 Hz per IEC 60068-2-6 — suitable for installation on machinery or in mobile equipment where shock and vibration are present.