National Electrical Code Articles and Information

1. [250.62]. Copper, aluminum, or copper-clad aluminum.
    

2. [250.64(A)]. Where in direct contact with masonry or the earth or in corrosive conditions. Don't terminate it within 18 inches of the earth.
    

3. [250.64(B)]. It must be "securely fastened to" that surface.
    

4. [250.64(C)]. Not normally, but yes if you meet one of two conditions specified in 250.64(C).
    

5. [250.64(D(3))]. The grounded conductor (of each enclosure) and the grounding electrode system.