Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A residential service entrance conductor is being installed for a single-family dwelling with an estimated load of 150A. According to NEC Table 250.66, what is the minimum size aluminum Grounding Electrode Conductor (GEC) required if it is the sole connection to the grounding electrode system?
- ANo. 4 AWG
- BNo. 2/0 AWG
- CNo. 2 AWG
- DNo. 1/0 AWG
Show answer & explanationAnswer & explanation
Correct answer: C. No. 2 AWG
According to NEC Table 250.66, for a service entrance conductor of 150A, the minimum size aluminum grounding electrode conductor is No. 2 AWG. You find the 'Service or Feeder Conductor Size' in the table and match it to the 'Grounding Electrode Conductor Size' column for aluminum.
Why the other options are wrong
- A. No. 4 AWG aluminum is for service conductors up to 100A.
- B. No. 2/0 AWG aluminum is for service conductors up to 300A.
- D. No. 1/0 AWG aluminum is for service conductors up to 200A.
GEC Sizing (Service Entrance)
The minimum size of the Grounding Electrode Conductor (GEC) is determined by the size of the largest ungrounded service entrance conductor, as specified in NEC Table 250.66.
- GEC protects against lightning, surges, and stabilizes voltage.
- Size depends on the ampacity of the service conductors.
- Table 250.66 is the primary reference for GEC sizing.
- Different columns for copper and aluminum GECs.
Memory trick: GEC size links to Service wire, through Table 250.66.