Outside installations of aluminum or copper clad aluminum conductors for radio and television antenna systems shall not be installed within how many inches of the earth?

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Keeping outside antenna conductors made of aluminum or copper-clad aluminum at a minimum distance from the earth protects them from moisture, soil contact, and physical damage. Aluminum is more susceptible to corrosion when in direct contact with soil moisture, so raising the conductor at least 18 inches above grade reduces exposure to moisture and corrosive soil conditions and makes the run easier to inspect and service. It also minimizes the chance of accidental damage from digging, lawn care, or snow removal near the ground.

Shorter distances would leave the conductor more exposed to moisture and damage, increasing the risk of corrosion or insulation failure. A larger clearance isn’t required by this rule, so 18 inches is the specified minimum that provides adequate protection without being unnecessarily burdensome.