How far must aluminum and copper-clad aluminum equipment grounding conductors be from the earth when outside a building?

The requirement for the placement of aluminum and copper-clad aluminum equipment grounding conductors is designed to ensure safety and functionality. Grounding conductors must be buried at a depth that protects them from physical damage and ensures they are not exposed to environmental conditions that could compromise their integrity.

The correct answer indicates that these conductors should be a minimum of 18 inches underground when outside a building. This depth is established to balance both safety and practicality. It is deep enough to avoid disturbances from surface activity, such as landscaping or pedestrian traffic, while also being shallow enough to allow for ease of installation and maintenance.

Choosing a shallower depth could increase the risk of damage to the conductors, while a deeper placement may make it more challenging to retrieve or inspect them. Thus, 18 inches is considered a rational compromise that aligns with safety codes and best practices in grounding and bonding installations.