How far must the ground clamp be from the earth for an aluminum grounding electrode conductor?

The requirement for the distance between the ground clamp and the earth for an aluminum grounding electrode conductor is established in the National Electrical Code (NEC). According to Section 250.64, the distance that the ground clamp must be installed above the earth is specified to be at least 18 inches.

This ensures that the clamp is above any potential moisture or corrosion points that could affect the conductivity of the grounding system. Proper elevation helps maintain the integrity of the connection, allowing it to effectively perform its function in ensuring a safe and reliable electrical grounding system.

The other options specify distances that do not conform to this code requirement. Therefore, choosing 18 inches aligns with the NEC guidelines and contributes to ensuring a secure and effective grounding system.