A 6A B-curve breaker will trip instantly when a small motor starts. Not because there is a fault, but because the locked-rotor current (often 6–10 times full load) triggers the magnetic coil. The ABB S201-K6 solves this by raising the magnetic trip threshold to 8 times rated current — 48A — while keeping the thermal overload characteristic sensitive enough to protect the motor from sustained overcurrent.

What Fits Behind a 6A K Curve
Typical applications include small refrigeration compressors (up to about 1 kW), ventilation fans, circulating pumps, small workshop drills, and solenoid valves. Also suitable for control transformers and lighting circuits with high inrush from electronic ballasts or LED drivers with large input capacitors. The K characteristic is defined in DIN VDE 0660 for power circuits and motor protection.

Electrical and Mechanical Specs
The S201-K6 is a 1-pole device, 17.5mm wide, rated for 230/400V AC and 72V DC. Breaking capacity is 6kA (Icn per EN 60898-1). Terminals accept solid conductors up to 25mm² or stranded up to 16mm², with a tightening torque of 2.8 Nm. Operating temperature –25°C to +55°C, storage –40°C to +70°C. Mechanical and electrical endurance are both 20,000 cycles. The red-green contact position indicator gives instant visual feedback.

Where B Curve Would Fail
If you have ever replaced a 6A B-curve breaker because it tripped every time the compressor started, the K curve is your fix. It is not that the B curve was defective; it was doing its job by detecting what looked like a short circuit (48A would be 8×6A, but B curve trips at 3–5×In, or 18–30A). The K curve simply raises the bar, accepting the brief inrush while still tripping quickly on a real short circuit.

Installation Notes
The S201-K6 mounts on 35mm DIN rail per EN 60715. Supply can be from top or bottom. The device can be sealed in both ON and OFF positions. Auxiliary contacts (S2C-H6R, etc.) and shunt trips are available as add-on modules. Country of origin is Germany. EAN: 4016779507257. RoHS and SVHC compliant.

Don’t Confuse K with C or D
C curve trips at 5–10×In, D curve at 10–20×In. K curve sits between B and C in terms of magnetic threshold (8×In) but has a different thermal characteristic optimized for motor protection. For pure resistive loads with no inrush, stick with B. For moderate inrush (lighting, small transformers), C may suffice. For motors and pumps, K is often the better choice.