Journeyman Electrician Exam (NEC)Grounding and BondingEasy
A journeyman is installing a new 277/480-volt, 3-phase, 4-wire feeder to a subpanel in a commercial building. The feeder conductors are 3/0 AWG copper. What is the minimum size copper equipment grounding conductor required for this feeder, assuming the overcurrent device protecting the feeder is rated at 200 amperes, according to NEC® Table 250.122?
- ANo. 8 AWG
- BNo. 10 AWG
- CNo. 4 AWG
- DNo. 6 AWG
Show answer & explanationAnswer & explanation
Correct answer: D. No. 6 AWG
According to NEC® Table 250.122, for an overcurrent device rating of 200 amperes, the minimum size copper equipment grounding conductor required is No. 6 AWG.
Why the other options are wrong
- A. No. 8 AWG is for overcurrent devices up to 100A.
- B. No. 10 AWG is for overcurrent devices up to 60A.
- C. No. 4 AWG is for overcurrent devices up to 250A, which is larger than the minimum required for 200A.
EGC Sizing by OCPD Rating
The minimum size of an equipment grounding conductor is determined solely by the rating of the overcurrent protective device in the circuit, as specified in NEC® Table 250.122, not by the feeder conductor size.
- Reference NEC® Table 250.122.
- Based on the upstream overcurrent device rating.
- Feeder conductor size is irrelevant for EGC sizing per this table.
Memory trick: The EGC is sized by the breaker's bite, not the wire's might.