What it is and what it does
The Siemens SENTRON 5SY7220-8MA is a 2-pole miniature circuit breaker rated 20 A at 400 V AC, with a D tripping characteristic and a breaking capacity of 25 kA per IEC 60947-2. It is a magnetic-only trip unit — no thermal bimetal — so it responds to short-circuit faults only, not overloads. That makes it a fit for applications where upstream overload protection is already provided and you need fast, high-current interruption on the branch.
What the ratings mean for your panel
The 25 kA breaking capacity at 400 V AC means this breaker can safely interrupt fault currents up to that level without welding its contacts or cascading failure upstream. In a 400 V industrial panel with a high available fault current, that SCCR headroom is what keeps coordination intact. The D curve (10–20× In) is designed for loads with high inrush — think motor starters, transformers, or solenoid banks — where a B or C curve would nuisance-trip on startup. The 2-pole, 2-module (36 mm wide) body snaps onto a DIN rail and occupies two width units. Depth is 76 mm, installation depth 70 mm; height 90 mm. It seals with a lockable cover (sealable: yes) to prevent unauthorized operation. IP20 with connected conductors — fine inside a closed panel, not for washdown. Ambient range from -40 °C to 75 °C covers most industrial enclosures. The terminal accepts top and bottom combined conductors, so you can daisy-chain busbars without extra lugs.