standards and guidelines for communication sites - Radio And ...
standards and guidelines for communication sites - Radio And ... standards and guidelines for communication sites - Radio And ...
SPECIAL GROUNDING (EARTHING) SITUATIONS CHAPTER 4: EXTERNAL GROUNDING (EARTHING) FIGURE 4-70 GROUNDING ELECTRODE SYSTEM WITH GROUND PLATES NOTE: Extend radial grounding conductors as allowed by available soil. See “Radial (Counterpoise) Grounding Conductors” on page 4-24. • Installation of building radial grounding conductors in a trench extending away from the building at each corner. The radial grounding conductors shall be buried as deep as the soil will allow. The radial grounding conductors shall bond to the building ground ring using exothermic welding or listed irreversible high-compression fittings. The radial grounding conductors should be encased in a grounding electrode encasement material. A conductive concrete may be the best grounding electrode encasement material for use in shallow topsoil environments, since the conductive concrete would not require a covering of topsoil for protection. Each radial grounding conductor may have ground plates installed every 1.8 to 4.9 m (6 to 16 ft.) along its length. See Figure 4-71. • Installation of tower radial grounding conductors in a trench extending away from the tower and building. The radial grounding conductors shall be buried as deep as the soil will allow. The radial grounding conductors shall bond to the tower ground ring using exothermic welding or listed irreversible high-compression fittings. The radial grounding conductors should be encased in a grounding electrode encasement material. A conductive concrete may be the best grounding electrode encasement material for use in shallow topsoil environments, since the conductive concrete would not require a covering of topsoil for protection. Each radial grounding conductor may have ground plates installed every 1.8 to 4.9 m (6 to 16 ft.) along its length. See Figure 4-71. 4-98 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING (EARTHING) SITUATIONS COMMUNICATION A SITE VERTICAL GROUND PLATE GROUND RADIAL UFER GROUND FIGURE 4-71 GROUNDING ELECTRODE SYSTEM WITH GROUND PLATES AND RADIALS 4.11.7 GROUNDING (EARTHING) IN ARCTIC REGIONS It may be difficult to achieve an effective low resistance grounding (earthing) electrode system at sites located in arctic regions (or similar cold climates). In these cases, consultation with an engineering firm is recommended. The primary issue with achieving an effective grounding electrode system in arctic regions is making good contact with frozen high-resistivity soils. Where frozen high-resistivity soils are encountered, optimum grounding can only be accomplished by special attention to both surface and subsurface terrain. The resistivity of frozen soils can be 10 to 100 times greater than in the unfrozen state; therefore, seasonal changes in temperature and moisture greatly affect the resistance to earth of the grounding electrode system. (See Appendix B for additional information regarding soil resistivity changes as a function of temperature and moisture.) See MIL-HDBK-419-A Volume I, section 2.11.1 for additional information. Seasonal freezing accounts for an increase in grounding electrode system resistance. If frozen soil has a high resistivity, then providing larger electrodes reduces the resistance to earth. In arctic areas that generally have very shallow surface thaw layers, horizontal rods or conductors may be easier to install than driven rods and provide an equivalent resistance to earth. Whether to install multiple electrodes, or a single deep-driven rod, or horizontal conductors is usually dependent on soil conditions at the site and the economics of installation. See MIL-HDBK-419-A Volume I, section 2.11.1 for additional information. An option for an effective grounding electrode system may be to install electrolytic ground rods that are encased in a grounding electrode encasement material. See “Electrolytic Ground Rods” on page 4-16 and “Grounding (Earthing) Electrode Encasement Materials” on page 4-27. See MIL-HDBK-419-A Volume I, section 2.11.2 for additional information. 68P81089E50-B 9/1/05 4-99
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STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SPECIAL GROUNDING (EARTHING) SITUATIONS<br />
COMMUNICATION A SITE<br />
VERTICAL GROUND PLATE<br />
GROUND RADIAL<br />
UFER GROUND<br />
FIGURE 4-71 GROUNDING ELECTRODE SYSTEM WITH GROUND PLATES AND RADIALS<br />
4.11.7 GROUNDING (EARTHING) IN ARCTIC REGIONS<br />
It may be difficult to achieve an effective low resistance grounding (earthing) electrode system at <strong>sites</strong><br />
located in arctic regions (or similar cold climates). In these cases, consultation with an engineering firm<br />
is recommended. The primary issue with achieving an effective grounding electrode system in arctic<br />
regions is making good contact with frozen high-resistivity soils. Where frozen high-resistivity soils are<br />
encountered, optimum grounding can only be accomplished by special attention to both surface <strong>and</strong><br />
subsurface terrain. The resistivity of frozen soils can be 10 to 100 times greater than in the unfrozen<br />
state; there<strong>for</strong>e, seasonal changes in temperature <strong>and</strong> moisture greatly affect the resistance to earth of<br />
the grounding electrode system. (See Appendix B <strong>for</strong> additional in<strong>for</strong>mation regarding soil resistivity<br />
changes as a function of temperature <strong>and</strong> moisture.) See MIL-HDBK-419-A Volume I, section 2.11.1<br />
<strong>for</strong> additional in<strong>for</strong>mation.<br />
Seasonal freezing accounts <strong>for</strong> an increase in grounding electrode system resistance. If frozen soil has a<br />
high resistivity, then providing larger electrodes reduces the resistance to earth. In arctic areas that<br />
generally have very shallow surface thaw layers, horizontal rods or conductors may be easier to install<br />
than driven rods <strong>and</strong> provide an equivalent resistance to earth. Whether to install multiple electrodes, or<br />
a single deep-driven rod, or horizontal conductors is usually dependent on soil conditions at the site <strong>and</strong><br />
the economics of installation. See MIL-HDBK-419-A Volume I, section 2.11.1 <strong>for</strong> additional<br />
in<strong>for</strong>mation.<br />
An option <strong>for</strong> an effective grounding electrode system may be to install electrolytic ground rods that are<br />
encased in a grounding electrode encasement material. See “Electrolytic Ground Rods” on page 4-16<br />
<strong>and</strong> “Grounding (Earthing) Electrode Encasement Materials” on page 4-27. See MIL-HDBK-419-A<br />
Volume I, section 2.11.2 <strong>for</strong> additional in<strong>for</strong>mation.<br />
68P81089E50-B 9/1/05 4-99
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