What this breaker is and where it fits
The ABB S201-K8 is a single-pole miniature circuit breaker from the S200 series, rated 8 A with a K trip curve at 277 V AC. It interrupts faults up to 6 kA, which covers most branch circuits in control panels and distribution boards where the available fault current stays under that threshold. The K curve means it tolerates moderate inrush — think motor starters, transformers, or solenoid banks — without nuisance tripping, while still clearing a hard short fast enough to protect the downstream wiring. It snaps onto standard DIN rail. The 1-pole format handles a single-phase 277 V leg.
K curve — why it matters for the loads you actually see
A K-curve breaker sits between the standard C curve and the high-inrush D curve. It trips magnetically at roughly 8 to 12 times rated current, so at 8 A that's about 64 to 96 A instantaneous pickup. That's high enough to pass through a motor start or a transformer energization without popping, but low enough to catch a bolted fault before the wire insulation melts. In practice, this makes the S201-K8 a good fit for motor branch circuits, power supplies, and lighting ballasts — loads that draw a brief spike on startup but settle to a steady-state draw well under 8 A. Compare that to a C-curve sibling like the S201M-C10, which trips at 5 to 10 times rated current. At 10 A that's 50 to 100 A magnetic pickup — similar range but with a higher continuous rating and a different curve shape. If your panel was originally specified around a C curve and you're swapping in a K curve, the thermal trip (overload) behavior is similar; the difference is in the magnetic trip threshold for short circuits. For most motor and transformer loads the K curve is actually the better choice — it's less likely to nuisance-trip on inrush.
Compliance and documentation
The S201-K8 is UL 1077 recognized and CSA 22.2 certified as a supplemental protector.