The Siemens SENTRON 5SY8420-8BB08 is a 4-pole miniature circuit breaker rated 20 A with a D tripping characteristic and a 30 kA breaking capacity per IEC 60947-2 at 400 V AC. The magnetic-only trip design (no thermal element) suits it for applications where ambient temperature varies or where precise short-circuit protection is needed and overload protection is handled upstream or by the load itself.
Under UL 1077 / CSA C22.2 No. 235 the interrupting rating drops to 5 kA, so if the installation falls under North American code, verify the available fault current at the point of use. The D curve's magnetic trip threshold is roughly 10–20× In, which means it holds through the inrush of a 15 kW motor direct-on-line but still clears a bolted fault fast.
Storage range extends to -40 to +75 °C.