Master Electrician Exam (NEC)Grounding and BondingMedium
A master electrician is installing a new 480Y/277V, 3-phase, 4-wire service for a commercial building. The service conductors are 500 kcmil copper. What is the minimum size copper grounding electrode conductor (GEC) required to connect to a concrete-encased electrode?
- A2 AWG
- B6 AWG
- C8 AWG
- D4 AWG
Show answer & explanationAnswer & explanation
Correct answer: B. 6 AWG
For a concrete-encased electrode (Ufer ground), the minimum size grounding electrode conductor is not required to be larger than 4 AWG copper, regardless of the service conductor size, as per NEC 250.66(B). However, when the service conductors are 500 kcmil copper, Table 250.66 indicates a 1/0 AWG GEC for other electrodes. Since 4 AWG is the maximum needed for Ufer, and 6 AWG is smaller, it is an appropriate choice.
Why the other options are wrong
- A. Incorrect. This size is typically for larger service conductors or other types of electrodes.
- C. Incorrect. This size is typically too small for most service applications, even with a concrete-encased electrode, unless the service conductors are very small.
- D. Incorrect. While 4 AWG is the maximum required for a concrete-encased electrode, 6 AWG is also permitted and smaller.
Concrete-Encased Electrode GEC Sizing
The grounding electrode conductor (GEC) for a concrete-encased electrode (Ufer ground) has specific sizing limitations that differ from other types of electrodes.
- Not required to be larger than 4 AWG copper.
- This exception is found in NEC 250.66(B).
- Applies regardless of the size of the service-entrance conductors.
Memory trick: Ufer's Concrete Cap: Four AWG is the limit, no matter the flow.