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 copper grounding electrode conductor (GEC) required if the grounding electrode is a concrete-encased electrode?
- A2 AWG
- B6 AWG
- C8 AWG
- D4 AWG
Show answer & explanationAnswer & explanation
Correct answer: D. 4 AWG
According to NEC Table 250.66, for service entrance conductors of 3/0 AWG copper, the minimum size copper GEC is 4 AWG. Additionally, NEC 250.66(B) states that the portion of the GEC that is the sole connection to a concrete-encased electrode is not required to be larger than 4 AWG copper. Both rules align to 4 AWG copper.
Why the other options are wrong
- A. 2 AWG is larger than required.
- B. 6 AWG copper is the limit for a ground rod connection, but not for a concrete-encased electrode in this scenario.
- C. 8 AWG copper is too small for 3/0 AWG service conductors per Table 250.66, and not the maximum for a concrete-encased electrode.
GEC Sizing for Concrete-Encased Electrode
The specific sizing requirement for the grounding electrode conductor when a concrete-encased electrode (UFER ground) is used, often limiting the conductor size to 4 AWG.
- Reference NEC 250.66(B).
- Maximum size typically 4 AWG copper for a concrete-encased electrode connection.
- Provides an effective, low-resistance ground.
Memory trick: UFER grounds are strong, but the GEC doesn't need to be bigger than a 'four' (AWG) for its connection.