Dave D'Epagnier wrote:
> Boy, I would think you'd want the ground grid to be as deep as
> reasonable because this grid may be dissapating all or part of the
> energy from a lightning strike. When I worked as an electrician in
> Wyoming on an industrial construction site the designs called for heavy
> copper cable ( about 1/2" dia) to be layed for the peripheral ground.
> We'd encircle the building with the cable, and cad-weld at right angles
> to this cable more cables that would enter the building at various
> places to be used as ground connections. As I recall these cables were
> about 4 to 6 feet deep in the soil, and about 6 to 8 feet away from the
> building foundation.
Most of the reason for the depth of burial on an industrial site is
related to mechanical protection issues over time ... if its under the
ground some one will dig it up the deeper you go though the longer it
takes to happen ( hopefuly ) The other reason for deep grounds are
soil conductivity and step voltage issues. Some industrial sites tend
to have very high availale fault levels often exceeding the current
levels found in most lightning strikes ... nothing wrong with a huge -
deep ground mat but a more modest ground system closer to the surface
with driven ground rods will do better than nothing..
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