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 Section 4:
INSTALLATION
4.1
General. Lightning protection systems shall be provided in
accordance with this manual.
4.2
Design Calculations. Design calculations shall consider earth
resistance and shall be based upon the soil resistivity for the specific
location. Computer programs are available and should be used whenever
possible. Project design criteria shall include names of approved computer
programs for use in design.
4.2.1
Earth Resistance. Maximum ground resistance for any lightning
protection system should not exceed 10 ohms. In high resistance soils or rock
formation, it may be necessary to provide ground counterpoises or artificial
grounds or to sink ground wells. After installation, each system shall be
tested by the single, direct reading instrument method. Where characteristics
are unknown, trial grounds should be installed and periodically tested during
the course of at least 1 year to include seasonal variations. Refer to
para. 4.5.2 for approved grounding methods.
4.2.2
Soil Resistivity. Project criteria will set forth the specific soil
resistivity values to be used for grounding system design.
4.3
NAVFAC Design Guides. For specific criteria and sample layouts for
systems, refer to NAVSEA OP-5, Vol. I, and Appendix A of this handbook.
4.4
Ordnance Facilities. Ordnance facilities shall be protected in
accordance with the following criteria: DOD-STD-6055.9; MIL-HDBK-419; NAVSEA
OP-5, Vol. I; NFPA 78; and Appendix A of this handbook.
4.4.1
Storage and Handling Facilities Above Ground. Provide a primary
protection system consisting of lightning masts or overhead conductors spaced
around the facility. Connect the masts and all metalwork in the vicinity,
such as railroad tracks, metal sheaths of underground cables, and metal piping
and conduits below ground that do not extend into the building or other
structure being protected, to the primary ground counterpoise. All railroad
tracks that extend into the building or structure shall also be grounded at a
minimum of 10 ft (3.05 m) from the building or structure.
4.4.2
Earth-Covered Magazines. Provide a secondary protection system.
Where a metal ventilator provides a salient point above the structure, mount a
pointed lightning rod on the ventilator and connect it to the secondary ground
counterpoise. A pointed lightning rod should also be mounted on the concrete
portal wall and connected to the secondary ground counterpoise. Bond together
reinforcing steel by wrapping it with wire and connecting it to the secondary
ground counterpoise.
4.4.3
Cranes on Piers and Wharves. Provide a primary protection system
consisting of overhead conductors spanned between structural supports and
connected to ground rods or to metal plates submersed in water.
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