What it is and what it does
The Siemens 5SL6303-7 is a SENTRON miniature circuit breaker — a 3-pole, C-curve unit rated at 3 A with a 6 kA breaking capacity under both EN 60898 and IEC 60947-2. That 6 kA figure means it can safely interrupt fault currents up to 6 kiloamperes without welding its contacts or cascading failure upstream, which is the standard for residential and light commercial distribution boards. The C-curve trips between 5 and 10 times rated current, so it handles moderate inrush from small motor loads or lighting ballasts without nuisance tripping.
Where it fits and how it mounts
Snaps onto a standard DIN rail — 3 modular width units (54 mm wide) — and accepts supplementary devices like shunt trips or auxiliary contacts. Mounting position is unrestricted, and the 70 mm installation depth leaves clearance behind the panel door. Rated IP20 with connected conductors, so it belongs inside a closed enclosure, not exposed to washdown.