Integrator's spec recap
The Siemens 5SY8663-8 is a SENTRON miniature circuit breaker in a 4-pole 3P+N configuration, D-curve, rated 63 A at 45 °C with a 20 kA breaking capacity per IEC 60947-2 at 400 V AC. The D characteristic (10–20× In) handles high inrush loads like motor starters and transformer primaries without nuisance tripping. Temperature range -40 to 75 °C, with derated current at higher ambients: 61.42 A at 50 °C, 59.79 A at 55 °C. That derate curve matters if the breaker sits near heat sources in a crowded cabinet.
Sourcing & fit
The 4-pole D-curve 63 A footprint is standard for motor branch circuits and high-inrush loads in industrial panels — verify the mounting rail and busbar spacing match your existing layout.