CSLB C-10 Electrical ContractorWiring Methods and MaterialsMedium
A residential service entrance requires a grounding electrode conductor (GEC) to connect the service equipment to a ground rod. The service is supplied by 2/0 AWG copper service-entrance conductors. What is the minimum size copper grounding electrode conductor required for this installation, according to NEC Table 250.66?
- A4 AWG copper
- B2 AWG copper
- C8 AWG copper
- D6 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: D. 6 AWG copper
According to NEC Table 250.66, for service-entrance conductors sized 2/0 AWG copper, the minimum size copper grounding electrode conductor (GEC) to a ground rod is 6 AWG copper. This table correlates the GEC size to the size of the largest ungrounded service-entrance conductor.
Why the other options are wrong
- A. 4 AWG copper is larger than required for this application.
- B. 2 AWG copper is significantly larger than required for this application.
- C. 8 AWG copper is too small for 2/0 AWG service-entrance conductors.
GEC Sizing (Table 250.66)
NEC Table 250.66 specifies the minimum size of the grounding electrode conductor (GEC) based on the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors.
- The GEC protects the electrical system from overvoltages and lightning.
- Different GEC sizes are required for connection to different types of grounding electrodes (e.g., ground rod, concrete-encased electrode, water pipe).
- The table provides separate columns for copper and aluminum/copper-clad aluminum GECs.
Memory trick: GEC size, for grounding's might, Table 250.66, sets it right!