How is motor overload protection selected according to NEC?

• A. Based on horsepower rating
• B. Based on conductor ampacity
• C. Based on the motor's full-load current (FLA) and applicable protection-device curves
• D. Based on voltage rating

Answer: (C)

Motor overload protection is chosen from the motor’s actual heat limit, not just its size. Start with the motor’s full-load current (FLA) from the nameplate and use the protection device’s time–current curve to set a device rating that will trip if the motor overheats, but allow the normal starting inrush. In other words, the protection must respond to sustained excess current over time (which heats the motor) while tolerating brief surge periods during startup. Horsepower alone doesn’t reflect the motor’s current draw, and conductor size or voltage rating aren’t the basis for sizing this protective function. The curves ensure proper coordination so the motor is protected without nuisance trips during normal operation.