The 5SY4340-6 is a 3-pole SENTRON miniature circuit breaker rated 40 A at 35 °C with a B tripping characteristic — meaning it trips at 3–5× rated current, suited for resistive and general-purpose loads where short-circuit protection is needed without nuisance trips from moderate inrush. Breaking capacity is 10 kA per IEC/EN 60898-1 and 15 kA per IEC 60947-2 / UL1077 — the higher figure under 60947-2 applies when the breaker is used in industrial distribution rather than final-circuit residential/commercial; that dual rating gives the specifier one part for both duty classes. Temperature derating is published per degree: 38.42 A at 40 °C, 37.6 A at 45 °C, 36.76 A at 50 °C, 35.92 A at 55 °C, 35.04 A at 60 °C — if the panel ambient runs above 35 °C, the actual load limit drops; size the downstream load against the derated figure, not the 40 A nameplate.
Occupies 3 modular width units (54 mm) on DIN rail, depth 76 mm, installation depth 70 mm — fits standard 3-MW cutouts; the quick-assembly fastening method means it snaps onto the rail without tools and releases via a screwdriver slot.
Approvals cover IEC/EN 60898-1, IEC/EN 60947-2, and UL1077 — accepted in European, UKCA, and North American industrial panels; halogen-free and silicon-free construction meets clean-environment specs for semiconductor or food-grade zones.