Siemens SENTRON 5SY8403-7 — 4-pole C-curve MCB, 3 A, 50 kA
The Siemens SENTRON 5SY8403-7 is a 4-pole miniature circuit breaker (MCB) with a C tripping characteristic, rated at 3 A at AC and offering a 50 kA breaking capacity at AC per IEC 60947-2. It is designed for panel mounting in industrial and commercial distribution boards, protecting circuits against overloads and short circuits up to that fault level. The IP20 protection rating with connected conductors applies once wired inside an enclosure.
That is a high-interrupting rating for a 3 A MCB, giving strong selectivity headroom in a distribution panel where fault currents can be substantial. The DC breaking capacity is 15 kA per the same standard, so it also handles DC circuits in the same panel. The 3 A rating is temperature-sensitive: at 45 °C it holds at 3 A, but at 50 °C it derates to 2.92 A, and at 55 °C to 2.85 A. The ambient temperature range itself is wide: -40 to 75 °C, so it is fine in unheated enclosures or near hot equipment as long as the load current is adjusted.
Vibration resistance per IEC 60068-2-6 is ±1 mm at 5 to 25 Hz and 50 m/s² at 25 to 150 Hz, which covers typical industrial panel vibration from nearby motors and conveyors. The halogen-free and silicon-free construction is relevant for environments sensitive to outgassing — clean rooms, semiconductor fabs, or food processing areas where silicone contamination is a concern.