What the ratings mean for fit
The S201-K40 is a single-pole miniature circuit breaker from the S200 series, rated 40 A continuous at 277 V AC line-to-neutral. The K-curve trips magnetically between 10× and 14× rated current — faster than a C-curve on moderate overloads, slower than a Z-curve. That characteristic suits motor-starting and transformer inrush loads where a brief current surge should not nuisance-trip the branch, but a hard fault still clears within the 6 kA interrupting rating. The 6 kAIC at 277 V AC is the maximum fault current the breaker can safely interrupt; any prospective fault above that requires an upstream current-limiting device.
Panel integration and deployment
Snaps onto standard 35 mm DIN rail — one module width (17.5 mm). Rated 277 V AC line-to-neutral, so it fits single-phase branch circuits in 480Y/277 V wye panels as a supplemental protector per UL 1077. CSA 22.2 listed alongside the UL mark, covering Canadian panel builds. The 40 A rating and K-curve make it a common choice for motor control center feeder protection or HVAC compressor circuits where the inrush profile exceeds what a C-curve allows.