The Siemens 5SY4540-7CV is a 1P+N miniature circuit breaker rated C40 with a breaking capacity Icu of 15 kA at 230/400 V. That 15 kA rating means it can safely interrupt a fault current up to that level without welding its contacts or cascading the fault upstream — a key spec for panel builders sizing the SCCR on a distribution board. The C-curve (40 A) trips between 5 and 10 times rated current, so it handles motor inrush and transformer energization without nuisance trips while still clearing short circuits fast.
Snaps onto standard DIN rail in a distribution panel or sub-board. The 1P+N form factor (single-pole switched plus neutral bar) saves one module width versus a 2-pole breaker when the neutral only needs isolation, not overcurrent protection — a common choice for single-phase final subcircuits in European-style panels.