New York State Master Electrician Practice Exam

What ampacity is required for branch circuit conductors supplying a single motor used continuously?

1. 100% of the motor's full-load current

2. 110% of the motor's full-load current

3. 125% of the motor's full-load current

4. 150% of the motor's full-load current

The correct answer is: 125% of the motor's full-load current

The correct choice is the requirement for branch circuit conductors supplying a single motor that is expected to operate continuously. According to the National Electrical Code (NEC), when determining the ampacity for branch circuit conductors to a continuous motor load, the conductors must be sized to accommodate at least 125% of the motor's full-load current. This consideration ensures that the conductors can handle the heat generated during prolonged operation and prevents overheating, which can lead to conductor failure or fire hazards. Motors can draw significant current, especially under continuous operation, so it is crucial to provide a safety margin above the rated full-load current. By sizing the conductors to 125%, this allows for additional capacity without exceeding the thermal limits of the wiring and reduces the risk of tripping circuit breakers or reducing efficiency. In this case, while some options may suggest 100% or 110% of the motor’s full-load current, those figures do not account for the necessary safety factor for continuous operation, making them insufficient for proper conductor sizing. The option stating 150% may also correspond to some applications, but the standard for continuous operation specifically calls for the 125% guideline. Thus, sizing to 125% is the industry standard for ensuring the safe