The Siemens 5SY4403-8CV is a miniature circuit breaker (MCB) rated for an ultimate breaking capacity Icu of 15 kA at 400 V AC, configured as a 4-pole unit with a D3 tripping characteristic.
Rated for 15 kA at 400 V, it handles high prospective fault currents typical of industrial panel main feeders or sub-distribution boards. The D3 curve provides a 10–20× In magnetic trip threshold, suited for loads with high inrush like small transformers or motor starters.