The Eaton Moeller S271-K3 is a single-pole miniature circuit breaker with a K-trip characteristic, rated 3 A at 277 VAC.
What the K-curve rating means
The K-curve trips between 8× and 12× rated current (24–36 A instantaneous magnetic trip). That's tighter than a B-curve and faster than a C-curve — sized for motor-starting inrush or transformer primary protection without nuisance tripping on the magnetizing surge. At 3 A it covers small single-phase loads like contactor coils, solenoid valves, or control transformers up to about 720 VA.