What it is and what it does
The Siemens SENTRON 5SY4303-7CC11 is a 3-pole miniature circuit breaker (MCB) with a C tripping characteristic, rated for 3 A at 400 V AC. It's built for branch-circuit protection in industrial control panels, distribution boards, and railway applications. The C-curve means it trips between 5 and 10 times the rated current — standard for moderate inrush loads like small motors, transformers, and lighting banks where you need to ride through the startup surge without nuisance trips. Its 10 kA breaking capacity per EN 60898 at 400 V AC means it can safely interrupt a fault current up to that level — enough for most downstream sub-distribution in an industrial panel, provided the upstream device coordinates properly.
Key ratings and what they mean for fit
Rated 3 A continuous at 400 V AC, with multi-phase and single-phase operation up to 440 V AC. That's a 3-pole device for a 3-phase load or three independent single-phase circuits sharing a common trip. It also carries a DC rating of 72 V maximum — useful for DC control circuits in the same panel, but note the voltage limit is lower than the AC rating. Pollution degree 3 and overvoltage category III mean it's rated for the harsh electrical environment inside an industrial enclosure — not just clean office distribution. The IP20 rating (with connected conductors) is standard for panel-mount gear; it's not meant for wet or dusty locations without an enclosure.
Mounting and panel integration
Mounts on a DIN rail via the quick assembly system — snap it on, no tools needed. Occupies 3 width units (54 mm wide). Installation depth is 70 mm, overall depth 76 mm. Height is 90 mm. Works in any mounting position. Combined terminals at top and bottom accept conductors; the device is sealable and touch-protected. Halogen-free and silicon-free construction matters if the panel is in a clean room or near sensitive electronics.