The Siemens 5SY7303-8 is a SENTRON miniature circuit breaker (MCB) with a D tripping characteristic, three poles, and a rated short-circuit capacity of 15 kA per EN 60898-1 or 40 kA per IEC 60947-2. The 40 kA rating under 60947-2 gives you headroom for industrial panels with high available fault current; the 15 kA EN rating covers the residential and light commercial path. It's rated for 400 V AC (440 V max in multi-phase or single-phase operation) and 60 V DC (72 V max).
Where it lives in the panel
Depth is 76 mm (70 mm installation depth). Combined terminals top and bottom simplify busbar or ring-tongue wiring.
Dual-rated to IEC / EN 60898-1 and IEC / EN 60947-2, plus UL 1077 and CSA C22.2 No. 235 (5 kA at AC). Halogen-free and silicon-free construction, which matters for outgassing-sensitive environments like clean rooms or sealed enclosures. Vibration resistance per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz — it holds up on a machine frame or in a mobile installation.