The Siemens SENTRON 5SY8320-8 is a 3-pole miniature circuit breaker with a D tripping curve, rated 20 A at 440 V AC and capable of interrupting 30 kA under IEC 60947-2. That 30 kA SCCR figure — not the 10 kA common on residential MCBs — tells you it can be used at the service entrance of an industrial panel where fault current runs high, without needing a current-limiting upstream breaker to protect it. The 3-pole design switches all three phases; neutral is not switched. Operating frequency is 50/60 Hz, so it fits standard line supplies worldwide.
At 45 °C ambient the breaker holds its full 20 A rating. At 50 °C it derates to 19.5 A; at 55 °C it drops to 18.98 A. The permissible operating range spans −40 °C to 75 °C, with humidity limits scaling from 95 % at 55 °C down to 35 % at 75 °C. For a panel builder that means if the breaker lives next to a heat source, you must account for the reduced current-carrying capacity — especially in a sealed enclosure.
Mounting position is any orientation. Halogen-free and silicon-free construction matters in environments where outgassing can contaminate contacts or optics — food processing lines, medical device manufacturing, or semiconductor cleanrooms. The breaker is also sealable, allowing the panel to be locked against unauthorized operation after commissioning.