Which material is NOT allowed for grounding electrode conductors when installed outside?

In grounding and bonding practices, the choice of materials for grounding electrode conductors is critical for ensuring safety and effectiveness. When it comes to installations outside, galvanized steel is not permitted for grounding electrode conductors due to its susceptibility to corrosion when exposed to outdoor elements.

Corrosion can lead to the deterioration of the conductor, reducing its effectiveness in carrying fault current to ground and potentially creating a safety hazard. On the other hand, aluminum, copper, and copper-clad aluminum are materials that can be used for grounding purposes because they have good conductivity and resistance to corrosion, especially when properly treated or coated.

Using materials that are appropriate for environmental conditions helps maintain the reliability of the grounding system and ensures compliance with the National Electrical Code (NEC) requirements. Therefore, the choice of galvanized steel as a grounding electrode conductor for outdoor applications is restricted to prevent safety risks associated with corrosion.