The ABB S201DC-K4 is a 1-pole miniature circuit breaker (MCB) with a Trip Curve K characteristic, rated at 4 A for both 60 V DC and AC circuits. It mounts on a standard DIN rail and provides 10 kA interrupting capacity. The K curve is specifically designed for DC applications and inductive loads — it holds through moderate inrush without nuisance tripping, then clears fast on hard faults. This is the curve to reach for when protecting DC motor circuits, solenoid valves, or control transformers where a C curve might trip on startup current and a Z curve would be too slow on a dead short.
What the ratings mean for fit
The 4 A rating at 60 V DC is the continuous current the breaker carries without heating. The Trip Curve K means magnetic trip occurs at 8–12× rated current (32–48 A), which is higher than a C curve (5–10×) but lower than a D curve (10–20×). This makes it suitable for loads with moderate inrush — DC motor starters, contactor coils, or power supplies that draw a short surge on energization. The 10 kA interrupting capacity at 60 V DC means it can safely clear a fault current up to that level without welding contacts or rupturing the case, which is sufficient for most control panel DC bus applications. The single-pole form factor snaps onto a DIN rail and occupies one modular width (17.5 mm).