What the ratings mean for the panel
The Siemens 5SY5440-6 is a 4-pole SENTRON miniature circuit breaker with a B tripping characteristic, rated 10 kA breaking capacity per IEC/EN 60898-2 and also listed under UL 1077. The B-curve means it trips magnetically at 3 to 5 times rated current — designed for resistive and general-purpose loads where inrush isn't severe, like lighting circuits, control transformers, and distribution subfeeds. The 10 kA rating at 400 V AC tells you it can safely interrupt a fault current up to that level without welding contacts or cascading upstream — critical for selectivity studies on a panelboard. It's rated for universal current (AC/DC), so it handles DC circuits up to 880 V per pole, but note the polarity requirement: on DC you must observe polarity as marked, which is a common gotcha on DC breakers that don't have a neutral-switching pole.
Integration and mounting
Snaps onto a DIN rail via the quick-assembly system — 4 modular width units (72 mm wide). Depth is 76 mm, installation depth 70 mm, so it fits standard distribution boards with the cover on. Mounting position any, which simplifies layout in tight enclosures. The combined top and bottom terminals accept both busbar and conductor connections, and the breaker is sealable for anti-tamper requirements. IP20 with connected conductors — fine for enclosed panels, not for washdown areas.