The Siemens 5SY6104-8CC is a 1-pole SENTRON miniature circuit breaker with a D tripping characteristic, rated 4 A at 35 °C and 440 V AC single- or multi-phase. It breaks 6 kA per EN 60898 and carries a 5 kA interrupting rating under UL 1077 / CSA C22.2 No. 235. This one sits on a DIN rail, takes one modular width unit (18 mm), and mounts in any position. It's sealable, halogen-free, and silicon-free, so it's fine for clean-room or food-line panels where outgassing matters.
Temperature derating — the number that really matters
The 4 A rating holds only up to 35 °C. At 40 °C it's 3.76 A; at 50 °C it's 3.5 A; at 55 °C it's 3.37 A. If your panel runs hot — and most industrial enclosures do — you need to size up one breaker or accept the reduced continuous current. This is the spec that trips up a BOM transfer from a 35 °C datasheet to a 50 °C panel.