Journeyman Electrician Exam (NEC)Services, Feeders, and Branch CircuitsEasy
A dwelling unit has a 200-ampere, 120/240V, single-phase service. What is the minimum size aluminum grounding electrode conductor (GEC) required to connect to a concrete-encased electrode?
- ANo. 6 AWG copper
- BNo. 4 AWG copper
- CNo. 2 AWG aluminum
- DNo. 1/0 AWG aluminum
Show answer & explanationAnswer & explanation
Correct answer: C. No. 2 AWG aluminum
For a service with 200-ampere overcurrent protection, the minimum size copper grounding electrode conductor (GEC) is No. 4 AWG. When using aluminum conductors, the equivalent size is No. 2 AWG. This is based on NEC Table 250.66.
Why the other options are wrong
- A. No. 6 AWG copper is typically used for ground rods or smaller services.
- B. No. 4 AWG copper is correct for copper, but the question specifies aluminum.
- D. No. 1/0 AWG aluminum is larger than necessary for this application.
GEC Sizing (Concrete-Encased Electrode)
The minimum size of a grounding electrode conductor (GEC) for a concrete-encased electrode is determined by the size of the service entrance conductors or the overcurrent protection of the service, as per NEC Table 250.66.
- NEC Table 250.66 is used for sizing GECs.
- Concrete-encased electrodes typically require a larger GEC than ground rods.
- Aluminum conductors require a larger gauge than copper for the same ampacity.
Memory trick: Grounding Electrode Conductors need careful sizing for safety.