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Lightning Rod Question


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Today's job was a large home on a ridge, and the home was equipped with a lightning rod system. I traced the wires down to ensure that they were still attached to buried ground rods. About 8 feet away from one of the rods at the end of the building was the gas meter. The meter had its original grounding rod and wire still intact. But the installer of the lightning rod system ran a jumper wire from his rod to the house side of the gas line, bonding them together. It is extremely rare for me to see lightning rods, but this strikes me as odd. It seems to me as though you're simply increasing the chances that you are going to electrify the gas piping, and even with its own ground rod I can't see that as a good idea.

So am I wrong or is this a bad idea?

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I don't know what the codes say about it but if confronted with such a condition, I wouldn't care. It's wrong. Lightning currents can cause voltage gradients in the earth. Rods used for lightning systems shouldn't be bonded to other electrical systems. To do so is to couple transitory voltages into them.

Marc

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This should stay on topic and not become a debate about the effectiveness of a properly installed lightning protection system.

Kevin,

It is required by NFPA 780, UL96A & LPI-175. If the municipality has not adopted NFPA 780, I think it's also in the newest edition of NFPA 54 (National Fuel Gas Code). It reads:

"Where a lightning protection system is installed for the structure, metallic gas piping shall be bonded to the lightning protection grounding system from a point downstream of the customer's meter..."

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The down conductors of lightning protection systems should be kept at least 6 feet away from metal parts of electrical equipment (like service masts) to prevent sideflash. The electrode for the lightning protection system is required to be bonded the grounding electrode system of the house power (NEC 250.106).

What you saw is very similar to the bonding requirement we now have for CSST, and probably using the same logic. If the earth voltage is elevated, you want ALL the metal systems in the structure to rise to the same voltage - you don't want there to be a large potential between them within the structure.

There's nothing wrong with the bond to the house side of the gas line. It sounds like the bond to the house power system might be what's missing.

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