What is the minimum size of a circuit breaker to be used for a 40A motor full load current?

The minimum size of a circuit breaker for a motor is determined by considering the full load current of the motor and applying the appropriate factors for motor protection as outlined in the National Electrical Code (NEC) and other electrical standards.

In this case, a 40A motor full load current would typically require a circuit breaker that can handle inrush currents and provide adequate protection for motor starting conditions. According to the standards, the recommendation is to size the circuit breaker at not less than 125% of the full load current. When you calculate 125% of 40A, you arrive at 50A, which is a minimum required value for the circuit breaker to ensure reliable operation without nuisance tripping.

However, the provided answer states that the correct size is 100AT, which would not comply with the standard sizing recommendations for protection of a motor with a full load current of 40A. Thus, the most technically accurate answer should align with the guideline of using a breaker sized at 125% of the motor's full load current, suggesting that the answer should reflect this practice rather than specify 100AT, which significantly exceeds the necessary requirement for protection and could lead to unsafe conditions.

Choosing a circuit breaker that is appropriately sized—no