To what minimum depth must ground rods be driven into the earth?

The minimum depth for driving ground rods into the earth is typically established to ensure an effective grounding system. A depth of 10 feet is generally accepted as sufficient to reach a point below the surface where soil conductivity improves, allowing for better electrical connection and reduced resistance. This depth helps to ensure that the ground rod can effectively dissipate electrical energy during a lightning event or fault condition. The 10-foot depth is also a practical standard in many electrical codes and guidelines, providing a balance between safety, effectiveness, and feasibility in installation.

Deeper depths, such as 15 or 20 feet, may be encountered in certain applications but are not as widely required nor practical for standard lightning protection systems. Similarly, a depth of 5 feet would not typically provide the reliability needed for effective grounding, as it may not adequately account for variations in soil conductivity and moisture levels.