MCB Curve B vs C vs D
เลือก curve ตามโหลดยังไง?

The curve is the current band that causes instantaneous (magnetic) tripping: B = 3-5× rated current (In), C = 5-10×, D = 10-20×. A higher curve tolerates more inrush before tripping — so you choose it by load type.

Curve B: resistive loads, lighting, heaters, and long cable runs. Curve C (the default): general mixed loads — sockets + lighting + equipment in buildings. Curve D: high-inrush loads such as motors, transformers, welders — B/C would trip on start-up.

Usually the curve is too low (B or C) for a load with start-up inrush (motor/transformer) — the inrush current exceeds the magnetic trip band, so it trips even without a fault. Fix by switching to curve D (10-20×), which tolerates inrush, while verifying the loop impedance (Zs) still trips in time on a real short circuit.

Yes — ABB S200/SH200 come in curves B, C, and D. Send the load type (lighting/sockets/motor + power) and rated current, and our team will match the curve and model. Genuine, factory pricing.