Master Electrician Exam (NEC)Services, Feeders, and Branch CircuitsMedium
A residential dwelling unit is being constructed with a 200A, 120/240V single-phase service. The service entrance conductors are 3/0 AWG copper. What is the minimum size required for the grounding electrode conductor (GEC) if the grounding electrode is a ground rod?
- A2 AWG copper
- B4 AWG copper
- C6 AWG copper
- D8 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: C. 6 AWG copper
According to NEC 250.66(A), a grounding electrode conductor used with a made electrode (like a ground rod) is not required to be larger than 6 AWG copper. This overrides the sizing from Table 250.66 based on the service conductors when a ground rod is the only electrode.
Why the other options are wrong
- A. This size is larger than the minimum required.
- B. This size is larger than the minimum required.
- D. This size is too small for a GEC to a ground rod.
GEC Sizing for Ground Rods
The grounding electrode conductor (GEC) connects the service equipment to the grounding electrode system, ensuring a connection to earth.
- Sizing generally follows NEC Table 250.66 based on service conductor size.
- For made electrodes (like ground rods), a specific maximum size limitation applies.
- NEC 250.66(A) limits the GEC to 6 AWG copper for ground rods.
Memory trick: GEC: service to earth, usually 6 AWG for rods.