The ABB S201M-C40 is a single-pole miniature circuit breaker from the S200M series, rated 40 A with a Trip Curve C characteristic.
40 A continuous current at 40 °C ambient — this is the thermal rating that governs the wire size (typically 8 AWG Cu for 75 °C terminals) and the load it can carry without nuisance tripping. Curve C means the magnetic trip fires at 5 to 10 times the rated current (200 to 400 A), so it handles moderate inrush from small motors, transformers, or capacitor banks without popping on startup. The 277 VAC rating is line-to-neutral for 277/480 Y systems common in North American commercial lighting panels. On the DC side, 60 VDC at 10 kA interrupting capacity covers control power supplies and battery circuits — a useful edge over the AC-only breakers in this footprint.