The ABB S201P-C2 is a 1-pole miniature circuit breaker rated 2 A with a Trip Curve C characteristic, interrupting 10 kA at 277 VAC.
The 1-pole width (roughly 18 mm per pole) keeps the panel layout tight; a 2 A C-curve breaker in this slot coordinates with downstream loads that don't exceed the 2 A continuous rating. No special busbar or adapter needed — standard comb busbars for the S200 series fit directly.
