The Siemens 5SY4420-8CV is a 4-pole miniature circuit breaker rated for a 20 A D-curve trip characteristic, with a 15 kA breaking capacity at 400 V. The D-curve means it tolerates the high inrush of motor loads or transformers without nuisance tripping — the magnetic trip threshold sits around 10–20× rated current, so it's a fit for inductive circuits where a B- or C-curve would drop out on startup. The 15 kA Icu at 400 V gives enough fault-current headroom for most industrial panelboards tied to a transformer secondary or a generator bus.
The 4-pole D20 configuration covers three-phase plus neutral switching, common in European-style distribution boards or machine control panels where the neutral needs overcurrent protection. The 15 kA SCCR at 400 V means it can be installed downstream of a larger main breaker without worrying about the fault current exceeding the breaker's rating — coordination stays clean.