The Siemens 5SY4340-6CC11 is a 3-pole SENTRON miniature circuit breaker rated 40 A with a B tripping characteristic and a 10 kA breaking capacity per EN 60898 at 400 V AC. It snaps onto a DIN rail (quick assembly system) and occupies 3 width units (54 mm) — standard panel real estate for a 3P breaker.
The B-curve (tripping characteristic class B) means the magnetic trip activates at 3 to 5 times rated current — so between 120 A and 200 A for this 40 A unit. The 10 kA breaking capacity at 400 V AC (per EN 60898) tells you this breaker can safely interrupt a fault current up to 10,000 A without welding its contacts or cascading damage upstream. That's sufficient for most secondary distribution boards fed by a transformer of typical impedance. Rated for 50/60 Hz operation, the 5SY4340-6CC11 also carries a maximum DC voltage rating of 72 V — useful if the same panel has a DC bus or control voltage that needs branch protection, though the AC rating is the primary spec.