What is the required size for the below-ground external grounding conductor?

• A. #4 AWG copper
• B. #2 AWG copper
• C. #1 AWG copper
• D. #6 AWG copper

Answer: (B)

Sizing the below-ground external grounding conductor focuses on giving a low-impedance path to earth so fault currents are carried safely and protective devices trip quickly. In this practice, the buried external grounding conductor is specified as two AWG copper. That size provides a reliable current path and keeps impedance low enough under typical soil and moisture conditions, which helps limit potential rises and ensures fast clearance of faults. Smaller sizes would have higher resistance and could allow higher voltages to appear on equipment grounds or slow down fault clearing, while a larger size like #1 would be more than necessary and add unnecessary cost. Using two AWG copper hits the balance between safety and economy for most installations.