Each plate electrode shall expose not less than how many square feet of surface to exterior soil, and shall be installed not less than how far below the surface of the earth?

• A. 2 below permanent moisture
• B. 1 21/2 ft
• C. 2 21/2 ft
• D. 1 below permanent moisture

Answer: (A)

Plate electrodes work by transferring fault current into the earth, so both the contact area with soil and the depth they’re buried matter. A plate electrode needs enough surface area in contact with exterior soil to keep earth resistance reasonable; the minimum is 2 square feet. You also want the electrode buried deep enough to be in consistently moist soil, which lowers resistance and keeps performance reliable year-round. That’s why the right requirement is exposing at least 2 square feet of surface to soil and installing it not less than the depth to reach permanent moisture. The other options either give an incorrect surface area or an inappropriate burial depth, which would reduce effectiveness and may not meet code.