CSLB C-10 Electrical ContractorWiring Methods and MaterialsMedium
A residential service entrance requires a grounding electrode conductor (GEC) to connect to a concrete-encased electrode (Ufer ground). The service entrance conductors are 4/0 AWG copper. What is the minimum size copper GEC required for this installation, according to NEC Table 250.66?
- A1/0 AWG copper
- B4 AWG copper
- C6 AWG copper
- D2 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: B. 4 AWG copper
According to NEC Table 250.66, for a concrete-encased electrode, the minimum size copper grounding electrode conductor must not be smaller than 4 AWG. This is a specific rule for Ufer grounds regardless of the service conductor size, as long as the service conductors are not extremely large.
Why the other options are wrong
- A. 1/0 AWG would be significantly oversized and not the minimum required.
- C. 6 AWG is typically for ground rods or pipe electrodes, not concrete-encased electrodes.
- D. 2 AWG would be oversized for this application and not the minimum required.
GEC Sizing (Concrete-Encased Electrode)
The sizing of a Grounding Electrode Conductor (GEC) connected to a concrete-encased electrode (Ufer ground) has a specific minimum requirement of 4 AWG copper, irrespective of the service conductor size, as long as the service conductors are not exceptionally large.
- Refer to NEC Table 250.66
- Concrete-encased electrodes (Ufer grounds) have specific GEC sizing rules
- Minimum 4 AWG copper for Ufer ground
Memory trick: Grounding Electrodes: Match the Metal to the Method.