The Siemens SENTRON 5SY4603-5 is a 4-pole miniature circuit breaker (3P+N) rated 3 A with tripping characteristic A, designed for 400 V AC systems. The A characteristic means it trips on short-circuit with minimal delay — suited for protecting semiconductor circuits or long cable runs where fast clearing is needed.
The 3 A rated operational current governs the continuous load — size upstream protection and cable accordingly. For DC circuits, it's rated 15 kA at 72 V per IEC 60947-2, and under UL 1077/CSA C22.2 No. 235 it carries 5 kA — useful if the panel ships to North America.