What this MCB is and what the ratings mean for fit
The ABB S203PR-K30 is a 3-pole miniature circuit breaker rated 30 A with a Trip Curve K characteristic. The magnetic trip threshold sits between 8x and 12x In. Rated 277 VAC line-to-neutral (or 480Y/277 V wye systems) and carries a 10 kA interrupting rating per IEC 60898 / EN 60898 — that's the standard for household and similar installations, so it's certified for the typical 10 kA prospective fault current you'd see in a North American light-industrial panel fed from a 75 kVA transformer. The 10 kA figure means it will safely clear a bolted fault up to that level without welding its contacts or venting arc gas into the enclosure. Mounts on a standard DIN rail (35 mm per EN 60715) and snaps into a 3-module-wide footprint. If you're swapping out a failed breaker in an existing panel, the DIN-rail clip and tunnel terminals (compatible with 1–25 mm² conductor) mean no panel rework — just lever the old unit off, clip the new one on, and torque the terminals. The S200PR RTT series shares the same physical envelope as the standard S200 family, so it drops into the same DIN space.