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jlmran 03-09-2011 10:08 PM

For the 'old timers'
Q1. A lot of older houses and barns were equipped with multiple lightning rods...located on the roof, and having heavy braided cable connecting the rods to some ground connection. Was this a NEC or other authoritative requirement or simply a common practice?

Q2. My hypothesis is that these rods may have 'invited' lightning strikes to the structure because of many elevated ground connections. Thoughts/facts about my hypothesis?

Do It Right 03-10-2011 06:54 AM

A few years ago I looked into adding lightning protection to a home we were building.
I had a long discussion with a gentleman from a Lightning Rod company.
My assumption was the same as yours, "lightning is going to hit the house because the rods are up there".
He assured me this is just NOT the case.
Lightning strikes occur whenever and wherever the static charges build up.
If your house offered the least resistance to the sky, it would strike whether or not the lightning rods were there.
If the closest tree offered less resistance, it might receive the hit.
The lightning rods help disperse the static charge to the sky without causing damage to your homes wiring system.

Another thing he mentioned, All metal that is within 10' of the rod or wire must also be bonded to it.
So at our house, that meant they (would have) had to bond the A/C system ductwork.
At the time he said two lightning rods installed (one at the top of each end of the house) bonded together, to two or four (can't remember) ground rods, (and bonding the attic ducting) would have been in the area of $3600.
We passed, hopefully the trees will take any hits.

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