The Siemens 5SY4302-8CC is a SENTRON miniature circuit breaker, 3-pole, D-curve, rated 2 A with a 10 kA breaking capacity at 400 V AC per EN 60898. This is the part for a panel line where you need a D-curve trip to handle high inrush from small motor or transformer loads — the D characteristic tolerates the momentary surge without nuisance tripping, then clears fast on a hard fault.
That standard covers household and similar installations; for industrial panels with higher available fault current, check the UL 1077 / CSA C22.2 No. 235 rating of 5 kA — that's the figure for North American acceptance. The D-curve means the magnetic trip fires at 10 to 20 times rated current, so a 2 A breaker trips magnetically between 20 A and 40 A. That's sized for loads like small control transformers or contactor coils that draw a brief inrush well above their running current. The DC rating tops out at 72 V, so this is an AC-only part in a 400 V panel. Three poles, no neutral switching — it breaks all three phases, but the neutral runs through. That's standard for a 3-phase motor or distribution subfeed where the neutral is bonded elsewhere. That's low enough that thermal buildup in a crowded enclosure is manageable, but if you're packing 20 of these in a row, the cumulative heat matters. Derate per the ambient curve: max 95% humidity up to 55 °C, dropping to 35% at 75 °C.
Width is 54 mm (3 modular units at 18 mm each), depth 76 mm, installation depth 70 mm. That's a standard 3-pole MCB footprint — drops into any DIN-rail enclosure that accepts 3-module-wide breakers. Sealable, halogen-free, silicon-free.