One or more metal in-ground support structures must be in direct contact with the earth for a minimum of how many feet to serve as a grounding electrode?

To serve as a grounding electrode, metal in-ground support structures must be buried in direct contact with the earth for a minimum of 10 feet. This requirement ensures that the grounding system has effective electrical contact with the ground, which is critical for safety and the proper functioning of electrical systems. The 10-foot depth allows for a sufficiently large surface area to facilitate the dissipation of electrical currents into the ground, reducing the risk of electrical shock and ensuring stable ground potential during fault conditions.

The regulations and standards set by organizations such as the National Electrical Code (NEC) specify this depth to help mitigate risks associated with lightning strikes or electrical faults. This depth is also practical to accommodate various soil conditions that may affect grounding effectiveness. Other options do not align with the established requirement of 10 feet, thus making it clear that a lesser depth would not provide sufficient grounding effectiveness under typical conditions.