It handles 277 VAC and 250 VDC circuits, with interrupting capacities of 6 kA on AC and 10 kA on DC. The K curve is the key spec here — it's designed for inductive and motor loads where inrush currents are higher than resistive loads, so it holds through the start-up spike without nuisance tripping, unlike a B or C curve that would drop out on a motor's first half-cycle.
Peer comparison
The closest sibling is the S201MUC-K2, which shares the same 1-pole DIN-rail footprint, same voltage ratings (277 VAC / 250 VDC), and same interrupting capacities (6 kA AC, 10 kA DC). The only difference is the current rating — 2 A vs 8 A. If your BOM line calls for an 8 A K-curve, the K2 won't substitute without a coordination review; the magnetic trip threshold scales with the amp rating, so the K2 trips at a lower overcurrent. Stick with the K8 for the 8 A slot.
Interrupting capacity in context
The 10 kA DC rating is useful for DC distribution in telecom or UPS downstream circuits.