The ABB S272-K4A is a 4 A miniature circuit breaker (MCB) in the S270 series, designed for snap-on mounting to a 35 mm DIN rail in a distribution board or control panel.
The 4 A rating is the continuous current the MCB carries without tripping; the K-curve trips between 10× and 14× rated current, which is sized for motor-starting inrush or transformer primary protection — not for general lighting or resistive loads (those want B or C curves). Because this is a DIN-rail MCB, it integrates into a standard enclosure with busbar feed and outgoing terminals; no special panel cutout or gland plate work needed beyond the rail.