Master Electrician Exam (NEC)Grounding and BondingEasy
A master electrician is installing a new 100A, 120/240V, single-phase service for a residential dwelling. The service entrance conductors are No. 1 AWG copper. What is the minimum size copper grounding electrode conductor required if the largest grounding electrode is a ground rod?
- ANo. 6 AWG
- BNo. 8 AWG
- CNo. 4 AWG
- DNo. 2 AWG
Show answer & explanationAnswer & explanation
Correct answer: A. No. 6 AWG
According to NEC Table 250.66, for service conductors No. 1 AWG copper, the minimum size copper grounding electrode conductor (GEC) is No. 6 AWG when connected to a ground rod, plate electrode, or concrete-encased electrode.
Why the other options are wrong
- B. No. 8 AWG is for smaller service conductors (e.g., up to No. 2 AWG copper service conductors), but not typically for 1 AWG when connected to a rod.
- C. No. 4 AWG is typically for larger service conductors (e.g., 2/0 AWG to 350 kcmil copper).
- D. No. 2 AWG is for very large services (e.g., 350 kcmil to 600 kcmil copper).
GEC Sizing (Specific Example)
For No. 1 AWG copper service conductors, the GEC to a ground rod is No. 6 AWG copper.
- Direct application of NEC Table 250.66.
- Common residential service size.
- Ensures adequate fault current path.
Memory trick: Number One service needs Six for the rod.