What is the minimum distance an aluminum or copper-clad aluminum grounding electrode conductor must be installed from the earth if it is external?

The minimum distance that an aluminum or copper-clad aluminum grounding electrode conductor must be installed from the earth when it is external is indeed 18 inches. This requirement is established to ensure that the conductor is installed in a manner that reduces the risk of physical damage and promotes greater safety. When grounding electrode conductors are installed at an adequate depth, they are less likely to be subjected to environmental effects such as corrosion or mechanical damage, which can compromise their effectiveness over time.

This specified distance safeguards the conductor from potential hazards while allowing it to perform its intended function of safely directing electrical faults into the ground. Installing the conductor at the proper depth is a best practice in grounding and bonding that enhances the overall reliability and durability of the grounding system.