Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsMedium
A commercial building requires a new 208-volt, 3-phase, 60-amp feeder circuit to a subpanel located 75 feet away. The circuit will use three 6 AWG THWN copper conductors for the phase conductors and one 10 AWG THWN copper conductor for the equipment grounding conductor. What is the minimum size of the equipment grounding conductor required for this feeder circuit?
- A8 AWG copper
- B4 AWG copper
- C6 AWG copper
- D10 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: D. 10 AWG copper
To determine the minimum size of the equipment grounding conductor (EGC) for a feeder, refer to NEC Table 250.122. For a 60-ampere overcurrent device, the minimum size copper EGC is 10 AWG. The feeder conductors being 6 AWG does not automatically mean the EGC must be 6 AWG; it is sized based on the overcurrent protective device rating.
Why the other options are wrong
- A. This is larger than the minimum required size.
- B. This is significantly larger than the minimum required size.
- C. This matches the phase conductor size but is not the minimum required for the EGC.
Feeder EGC Sizing
The determination of the minimum size for an equipment grounding conductor for a feeder circuit, based on the rating of the overcurrent protective device.
- Sized by the feeder's overcurrent protection.
- Ensures adequate fault current path.
- Found in NEC Table 250.122.
Memory trick: Overcurrent protection dictates the EGC's strong connection.