HOLT Electricians Practice Exam

Feeder overload protection must be sized based on which factor?

1. The voltage of the motors only

2. The largest branch circuit short circuit ground fault protection device of any motor in the group

3. The sum of all motor efficiencies

4. The ambient temperature conditions only

The correct answer is: The largest branch circuit short circuit ground fault protection device of any motor in the group

Feeder overload protection must be sized based on the largest branch circuit short circuit ground fault protection device of any motor in the group. This is essential because it ensures that the feeder is protected against overcurrent situations that could arise from any of the motors connected to it. In scenarios where multiple motors are fed by the same feeder, it is important to account for the worst-case scenario, which is typically represented by the largest protection device in the group. This approach helps prevent nuisance tripping and ensures that the feeder can handle the maximum potential load while still adequately protecting the individual motors from overload conditions. Sizing based on the largest branch circuit short circuit ground fault protection allows for the appropriate calibration of the feeder’s protective devices, ensuring that they coordinate properly with those on the downstream branch circuits. This coordination is crucial for minimizing downtime and potential damage to equipment in the event of a fault. Other factors, such as ambient temperature conditions, motor efficiencies, or just the voltage of the motors alone, do influence system performance but do not serve as the primary determination for sizing feeder overload protection, which is predominantly dictated by the characteristics of the largest branch circuit protection device in the motor group.