The ABB S201-C20 is a 1-pole miniature circuit breaker rated 20 A at 277 VAC with a Trip Curve C characteristic. The 20 A rating means it carries continuous loads up to that level before the thermal-magnetic trip mechanism engages — sized for branch circuits feeding moderate loads like lighting banks, small motors, or control transformers. The Trip Curve C trips between 5× and 10× rated current (100–200 A instantaneously), which is the standard choice for general-purpose distribution where you don't want nuisance trips from motor inrush but need fast clearing on hard faults. The 6 kA interrupting rating at 277 VAC tells you it can safely clear a short-circuit fault up to 6,000 A without welding contacts or rupturing the case — adequate for most commercial and light industrial panelboards where the available fault current stays under that threshold.
The single-pole footprint takes up one module width (17.5 mm), so it fits neatly into a crowded enclosure where space is tight. Terminal clamps accept up to 25 mm² conductor, which is oversized for a 20 A circuit but handy when you're tapping into a larger feeder.