Lightning and electrical contractors follow this general set of rules
1. All structures under 250 ft around should have at least 2 groundings.
2. If the structure is more than 250 ft around please add 1 ground per 100 ft.
3. Treat all structures the same whether they are metal buildings, timber framed barns, residential homes.
4. Cables need to be neatly laid out with no loops, dips, hard 90 degree turns.
5. Do not mix metal types! If you have copper roofs use copper hardware, cable, lightning rods and the same goes for Aluminum with aluminum roof applications.
6. Aluminum hardware should never be installed under the ground.
A. Space rods evenly, no more than 20 feet apart.
B. End rods should be no more than than 2 feet from the end (1 foot is typical).
C. Fasten cable every 3 feet.
D. Connect vents and antennas with clamp or lug if within 6 feet of the lightning wire.
E. For a neat job run the down cables next to down spouts, molding, etc. and connect to ground rods (make connection below ground).
REMEMBER: Each lightning protection installation is unique. The guidelines above are for general applications and it should not be assumed that these guidelines reflect the correct way to provide lightning protection for your structure.
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Links to other Lightning Protection Guidelines
UL (Underwriters Laboratories) Installation Guidelines
Residential Lightning Protection and Grounding
Arborist (Tree-Top) Lightning Protection and Grounding