HOLT Electricians Practice Exam

Are feeder conductors that supply several motors required to have an ampacity of at least 125% of the highest rated motor FLC?

1. True

2. False

3. Only if multiple motors are connected

4. Only for single-phase motors

The correct answer is: True

The requirement for feeder conductors that supply several motors to have an ampacity of at least 125% of the highest rated motor full load current (FLC) is grounded in the National Electrical Code (NEC) guidelines. This rule is established to ensure that the conductors can handle the load safely, considering potential increases in current draw when the motors start, especially since motors often have a higher inrush current compared to their running load. By sizing the conductors to at least 125% of the highest motor’s FLC, you provide a safety margin that accounts for the fact that motors may not operate at full load continuously. This practice helps prevent overheating of the conductors, which can lead to insulation damage and poses a risk of fire. It is essential when multiple motors are connected, as they are likely to operate alternately or under varying loads, and having more than enough capacity in the feeder conductors adds to the overall safety and reliability of the electrical system. This requirement applies to all motors regardless of phase type, making it a standard safety measure in electrical installations involving motors.