It is crucial to bond all outside grounding together to create an equipotential grounding system. This ensures that everything on-site is at the same electrical potential thus reducing dangerous and damaging voltage gradients. Generally, each grounding system should consist of a ground ring installed around the perimeter of the building and a means by which to lower ground resistance to meet the target resistance value. The ground resistance can be lowered by using ground rods, and vertical or horizontal enhanced electrodes. At the Sandia Research Lab, a U.S. Department of Energy laboratory, scientists studying triggered lightning have documented a constant characteristic.
Lightning tends to move horizontally along the earth once it makes contact, as shown above.
This research, coupled with ample evidence in nature, clearly indicates that lightning dissipates horizontally. As a result, grounding systems designed with horizontal electrodes are best suited to deal with lightning s horizontal dissipation characteristics. Vertically oriented grounding systems, for example ground rods, are not as effective for lightning protection. At many locations traditional grounding systems alone will not meet your grounding system requirements. Traditional systems may not be able to achieve your resistance targets, may not be able to dissipate high rise time surges, and may be subject to corrosion.