Ala. Code § 25-9-172: Grounding of Frames, Casings, and Other Electrical Equipment.

Where grounding wires are used to ground metallic sheaths, armors, conduits, frames, casings and other metallic enclosures, such grounding wires must comply with the following conditions:

(1) The cross-sectional area (size) of the grounding wire shall be at least one-half the cross-sectional area (size) of the power conductor where the power conductor used is No. 6 A.W.G. or larger.

(2) Where the power conductor used is less than No. 6 A.W.G., the cross-sectional area (size) of the grounding wire shall be equal to the cross-sectional area (size) of the power conductor.