The Siemens SENTRON 5SY6040-6KL is a 1-pole+N miniature circuit breaker rated 40 A at 230 V AC, with a B tripping characteristic and 6 kA breaking capacity certified to EN 60898. That B curve means the magnetic trip threshold sits between 3 and 5 times rated current — it clears moderate overloads fast enough for general-purpose resistive and light inductive loads, but won't nuisance-trip on the inrush of a motor branch unless the motor is very small. The 6 kA breaking capacity at 230 V AC covers the typical prospective short-circuit current at the final sub-distribution board in most commercial and residential installations; if your point of supply has a higher fault level, you'll need to verify coordination upstream.
Mounts on standard DIN rail (EN 60715) in any orientation — the 18 mm width (1 MW) fits one module slot, and the 70 mm installation depth leaves clearance for a standard enclosure backplate. The neutral pole switches internally (neutral conductor switching is a listed function), so you get a single-width unit that disconnects both L and N in the same housing. IP20 with connected conductors means it's protected against finger contact but not against moisture — keep it inside a panel or enclosure rated for the environment. Terminal capacity accepts up to 16 mm² solid or stranded copper.