The Siemens 5SY4320-8CC is a SENTRON 3-pole miniature circuit breaker with a D tripping characteristic, rated 20 A at 35 °C and 10 kA breaking capacity per EN 60898 at 440 V AC.
Thermal derating and environment
The 20 A rating holds at 35 °C ambient. At 40 °C it derates to 18.8 A, at 50 °C to 17.52 A, and at 55 °C to 16.84 A. The breaker also handles humidity up to 95% at 55 °C, tapering to 35% at 75 °C.
What it does and where it goes
As a miniature circuit breaker (MCB), it protects downstream wiring and loads against overloads and short circuits. The D curve is the key selection parameter: it's designed for circuits with high inrush — think motor feeders, solenoid banks, or small transformers in industrial control panels. The 3-pole configuration handles three-phase loads; there's no neutral pole switching, so the neutral must be connected separately if the circuit requires it.