Figure 5. Separately-mounted shielding system (mast type).
The height of this system ensures that the entire structure is enclosed in a zone of protection. This system is
separated at least 6 feet from the structure and is increased by 1 foot for every 10 feet of structure height above
50 feet.
Separately-Mounted Shielding Systems (Overhead-Wire Types)
The separately-mounted shielding system (overhead-wire type)(Figure 6) consists of grounded, elevated
horizontal metallic wires stretched between the mast surrounding the structure. This system minimizes
hazardous side flashes. This system is often recommended especially for structures with perimeters greater than
300 feet.
Grounding, Bonding, and Surge Protection
Grounding. When a ground rod is necessary a resistance of 10 ohms or less to ground for a lightning protection
system is the desired optimum. If ohms resistance cannot be achieved with ground rods alone, a counterpoise
system is acceptable even if it is greater than 10 ohms.
Bonding. The bonding of metallic bodies is required to ensure that voltage potentials due to lightning are equal
everywhere in the facility. The resistance of any metal object bonded to the lightning project is equal to 1 ohm
10 percent of the system.
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MM0149
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