Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsMedium
A residential electrician is installing a new 200-amp, 120/240-volt single-phase service entrance for a single-family dwelling. The service conductors are 3/0 AWG copper. What is the minimum size copper grounding electrode conductor (GEC) required if the grounding electrode is a ground rod?
- A4 AWG
- B2 AWG
- C6 AWG
- D8 AWG
Show answer & explanationAnswer & explanation
Correct answer: C. 6 AWG
According to NEC 250.66(A), the grounding electrode conductor for a concrete-encased electrode, ground rod, or plate electrode shall not be required to be larger than 6 AWG copper. While 3/0 AWG service conductors would normally require a 4 AWG GEC based on Table 250.66, the specific type of electrode (ground rod) allows for a smaller GEC size.
Why the other options are wrong
- A. Incorrect. While 4 AWG would be derived from Table 250.66 for 3/0 AWG service conductors, the exception for a ground rod (250.66(A)) allows for a smaller 6 AWG.
- B. Incorrect. This size is larger than required for a ground rod and would be used for larger service conductors without the ground rod exception.
- D. Incorrect. This size is too small; the minimum for a ground rod is 6 AWG.
GEC Sizing (Ground Rod Exception)
The NEC rule that allows a smaller minimum size for the grounding electrode conductor when a ground rod, concrete-encased electrode, or plate electrode is used.
- Applies to specific types of grounding electrodes.
- Overrides the general sizing from Table 250.66.
- Prevents unnecessarily large GECs for limited electrode performance.
Memory trick: Rod Rules Reduce Required Gauge.