Lightning Protection Ground Ring

[charlie b]

I am including a lighting protection system for a new, 3-story metal building. It will have a ground ring of bare 4/0, with the occasional ground rod along the path. UL96A says to install the ring a minimum of 2 feet from the foundation wall (no maximum distance is given), and at a minimum depth of 18 inches. This building has an external staircase, so the footings extend at least 6 feet from the perimeter of the building. There is less than 18 inches of dirt above the footings. So my plan is to dig the trench 2 to 4 feet beyond the footings, or as much as 10 feet from the building.

If the sole purpose of the ring is to carry a lightning strike into the dirt, that distance would not matter so much. But if this will also serve to establish an equipotential plane within a person?s reach of the building, 10 feet from the building will not answer.

Question: Is my plan acceptable, or is the (admittedly controversial) notion of an equipotential plane an important consideration?

 

[mgookin]

I am including a lighting protection system for a ...

I think you answered your own question. You're designing a lightning protection system. If your project does not require, and your client did not request, an equipotential plane then it should not be an issue.

If it's military or a defense contractor, they may have specs aside from local or state codes.

 

[steve66]

You could bond the ground ring to the foundation rebar every so often.

Also, just a suggestion, but the NEC has a minimum depth of 30" for a ground ring. You might want to spec. that depth just so it's a suitable grounding electrode per the nec too.