Siemens 5SY4240-8CV MCB, Icu=15kA 400V 2P D40

The Siemens 5SY4240-8CV is a 2-pole miniature circuit breaker with a D40 trip characteristic and a rated short-circuit breaking capacity Icu of 15 kA at 400 V AC. The D curve means it tolerates high inrush currents — the typical choice for motor, transformer, or lighting ballast circuits where the starting surge would nuisance-trip a B or C curve. The 15 kA Icu tells you it can safely interrupt a fault up to that level without welding contacts or cascading failure upstream, which matters when coordinating selectivity in a distribution board.