The Siemens 5SY4103-7CC is a 1-pole SENTRON miniature circuit breaker with a C-curve trip characteristic, rated 3 A at 230/400 V AC and a 10 kA breaking capacity per EN 60898. This is the part to specify when a 3 A C-curve MCB is called out on the BOM — no substitution guesswork.
The 10 kA breaking capacity at 230/400 V AC per EN 60898 means this breaker can safely interrupt a fault current up to 10 kA without welding its contacts or failing catastrophically — that covers most commercial and light industrial panelboards fed by a typical distribution transformer. It will not nuisance-trip on a motor start but will clear a hard short before the upstream feeder breaker sees it. Temperature derating is real on this part. At 40 °C ambient the 3 A rating drops to 2.76 A; at 50 °C it is 2.49 A. If the panel runs hot — say inside a sealed enclosure near a drive — size up one frame or account for the reduced continuous current. The IP20 rating applies only with connected conductors — the busbar stabs are live when the breaker is clipped on but unwired, so keep the panel door locked during commissioning.
Where it goes in the panel
One 18 mm module on a DIN rail, 76 mm deep behind the panel face — leaves room for wiring behind a 100 mm deep enclosure.