Lightning Protection - Arborist Guidelines
Adopted by the Tree Care Industry Association

Because lightning seeks the highest feature within sight of a given storm, trees become very susceptible to lightning strikes. We've all seen too many big, beautiful trees hit every year, trees like that big live oak or white pine in your own back yard.

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Tree Care Industry Association Standards
In August 2002, TCIA adopted the American National Systems Institute (ANSI) A300 standard (Part 4). A complete copy of the standard is available for purchase by contacting the TCIA office at 1-800-733-2622.

• Cable for Main Runs need to be a minimum of 14 strands of 17 gauge.
• Cable for Secondary Runs need to be a minimum of 14 strand of 17 gauge.
• Cable Fasteners need to be a minimum of every 6 feet.
• Canopy Coverage should have no aerial portion of the tree farther than 35 feet from any lightning rod or air terminal.

Grounding Recommendations • Trees Under or Over 36” diameter at base height. • Minimum of one main downlead cable and one ground rod • Ground Rod locations should be no less than 10 ft from the trunk. Trees recommended for grounding include those used by people for shelter in a storm; tall trees within 10 feet of a building; older, mature trees at parks and historic sites; and any larger trees on private property that have intrinsic value. Lightning control devices should be installed by professionals who follow detailed installation instructions. Annual inspections are necessary to make sure that all strands are intact. Expansion of the treetop terminals may necessary as the trees grow.

Links to other Lightning Protection Guidelines

UL (Underwriters Laboratories) Installation Guidelines
Residential Lightning Protection and Grounding
Barn and Outdoor Structure Lightning Protection and Grounding