Which material is not permitted as a wire-type grounding electrode conductor?

In grounding systems, the materials used for grounding electrode conductors are subject to specific standards and regulations. Steel is not permitted as a wire-type grounding electrode conductor primarily because it is prone to corrosion, especially when exposed to moisture and varying environmental conditions. The effectiveness of a grounding system relies not only on the conductivity of the material but also on its longevity and ability to resist environmental degradation over time.

Copper and aluminum are commonly used materials in grounding applications because they have excellent electrical conductivity and resistance to corrosion. Copper clad-aluminum is also accepted since it combines the benefits of both materials, featuring a conductive layer of copper over aluminum, which enhances its corrosion resistance while maintaining good conductivity.

Choosing steel for grounding would potentially jeopardize the reliability and safety of the grounding system, which is why it is not permitted.