The Siemens 5SY8203-8 is a SENTRON miniature circuit breaker (MCB) with a D tripping characteristic, rated 3 A at 45 °C ambient, 2-pole design, and a 50 kA breaking capacity per IEC 60947-2 at 440 V AC. At 50 °C the continuous rating derates to 2.91 A; at 55 °C it drops to 2.81 A. The part is rated for ambient humidity up to 95% at 55 °C, tapering to 35% at 75 °C. This matters when the breaker lives inside a non-ventilated enclosure near hot machinery — the real-world ampacity may be lower than the nameplate 3 A, so size the upstream protection accordingly. The DC side is rated 15 kA at 72 V maximum, so it also works in DC control circuits or battery-backed bus bars within that voltage ceiling.
The combined terminal at top and bottom accepts the same conductor range — no special feed-through lug needed. Halogen-free and silicon-free construction, sealable for lockout/tagout. Neutral conductor is not switched — this is a 2-pole breaker switching both phases (line and load side) but leaving the neutral bar continuous. The supply cord can enter from any position.