Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A residential garage is being built detached from the main dwelling unit. It will be supplied by a 60A feeder from the main house panel. The garage has a grounding electrode system consisting of two ground rods. What is the minimum size required for the grounding electrode conductor (GEC) from the garage subpanel to these ground rods?
- A8 AWG copper
- B4 AWG copper
- C2 AWG copper
- D6 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: D. 6 AWG copper
For a detached building's grounding electrode conductor, if the only electrode is a ground rod (a made electrode), the GEC is not required to be larger than 6 AWG copper, according to NEC 250.66(A). The feeder size does not directly determine the GEC size for ground rods, as 250.66(A) provides a specific maximum.
Why the other options are wrong
- A. This size is too small for a GEC to a ground rod.
- B. This size is larger than the minimum required.
- C. This size is larger than the minimum required.
GEC Sizing (Ground Rod Electrode)
The grounding electrode conductor (GEC) connects the service equipment or a separately derived system to the grounding electrode system.
- Sizing generally follows NEC Table 250.66 based on the largest ungrounded service or feeder conductor.
- For made electrodes like ground rods, a specific maximum size of 6 AWG copper applies.
- This 6 AWG limit applies regardless of the feeder or service conductor size.
Memory trick: Ground rod GEC: always a 6, copper, no bigger.