The Siemens 5SY4140-8CV is a 1-pole miniature circuit breaker (MCB) with a D40 tripping curve and a rated ultimate breaking capacity (Icu) of 15 kA at 230/400 V AC. The D curve is specified for loads with high inrush currents — motor starters, transformers, discharge lighting — where a B or C curve would nuisance-trip on the magnetizing surge. The 15 kA Icu at 400 V means it can safely interrupt a fault current up to that level without welding the contacts or cascading failure upstream; this matters for panel coordination studies where the prospective short-circuit current at the distribution board exceeds 10 kA.
Integration Note
Mounts on standard 35 mm DIN rail per EN 60715. The 1-pole width (1 module at 18 mm) fits a compact distribution board or final-sub-distribution panel. The D40 curve at 15 kA Icu coordinates with upstream SENTRON series NH fuse-links or SENTRON 3VL moulded-case breakers for selective tripping; verify the let-through energy (I²t) against the downstream load's withstand rating during panel design.