HOLT Electricians Practice Exam

How must the feeder overload protection be sized in relation to the motor’s specifications?

1. No specific relation

2. Above the motor’s full-load current

3. Not greater than the largest motor's branch circuit protection plus others

4. Equal to the total of all motor currents

The correct answer is: Not greater than the largest motor's branch circuit protection plus others

The correct answer focuses on the requirements set forth in the National Electrical Code (NEC) regarding feeder overload protection. Specifically, feeder overload protection must be carefully sized to ensure that it is capable of handling the largest motor's branch circuit protection, as well as any additional motors that may be operating simultaneously. This approach helps to prevent nuisance tripping while still providing adequate protection against overload conditions. When sizing the feeder overload protection, it must not exceed the maximum rating of the branch circuit protection for the largest motor, which allows for the coordination of protection devices. This coordination is crucial as it ensures that only the affected portion of the circuit will be de-energized in the event of an overload, thus maintaining the operation of other connected loads. In contrast, sizing the protection above the motor's full-load current or equal to the total of all motor currents does not comply with the NEC. Over-sizing can lead to inadequate protection of the motors, while not accounting for the specifics of each motor's branch circuit can also increase the risk of failures or damage during overload conditions. Therefore, choosing the sizing method aligned with the largest motor's branch circuit protection is optimal for safety and operational efficiency.