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STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING (EARTHING) REQUIREMENTS
4.7.7 DEDICATED COMMUNICATIONS BUILDING GROUNDING
(EARTHING)
All dedicated communications buildings shall have a properly installed external grounding (earthing)
electrode system. The grounding electrode system resistance shall meet the requirements of
“Grounding (Earthing) Electrode System Resistance Requirements” on page 4-46.
A typical site grounding electrode system layout is shown in Figure 4-4 on page 4-8. The building
grounding electrode system requirements are listed below and shall also include any additional
grounding electrode system components required to achieve the resistance requirements of the site. See
“Minimum Site Grounding (Earthing) Requirements” on page 4-44.
• Installation of concrete encased electrodes as part of new construction. See “Concrete-Encased
Electrodes” on page 4-20.
• The building shall be encircled by a ground ring installed in accordance with “External Building
and Tower Ground Ring” on page 4-22.
• The building ground ring shall have a ground rod installed near the external ground bus bar (EGB),
at each corner of the shelter, and as follows:
• If 2.4 m (8 ft.) ground rods are used, additional ground rods shall be installed as needed to
reduce the distance between rods from 3 m to 4.6 m (10 to 15 ft.) (ANSI T1.334-2002).
• If longer ground rods are used, a larger separation proportional to the increase in rod length
may be used.
• Ground rods shall be placed a minimum of one rod length apart along the ground rings (ANSI
T1.313-2003, figure 3(a)).
• Ground rods shall not be separated from an adjacent ground rod along the ground ring by more
than the sum of their respective lengths. (MIL-HDBK-419A).
• The ground rods shall be installed in accordance with “Ground Rods” on page 4-11.
• The ground rods shall be exothermically welded to the ground ring, or as otherwise allowed in
“Bonding to the External Grounding (Earthing) Electrode System” on page 4-40.
• The building ground ring shall be bonded to the tower ground ring using a minimum of two
35 mm 2 csa (#2 AWG) or coarser, bare, solid, tinned or un-tinned, copper conductors. See
“External Building and Tower Ground Ring” on page 4-22 and Figure 4-4 on page 4-8.
• The tower shall be grounded in accordance with “Tower Grounding (Earthing)” on page 4-50.
• Determine if radial grounding conductors should be installed at the site, see “Radial (Counterpoise)
Grounding Conductors” on page 4-24
4.7.7.1 GENERATORS EXTERNAL TO THE BUILDING
Generators installed outside of the building, within 1.8 m (6 ft.) of the building, shall be bonded to the
nearest practical location on the grounding (earthing) electrode system as shown in Figure 4-40 on
page 4-60, using a 16 mm 2 csa (#6 AWG) or coarser, copper conductor (ANSI T1.334-2002, section
5.3.3). Grounding conductors routed below ground, or partially below ground, shall be a 35 mm 2 csa
(#2 AWG) or coarser, bare, solid, tinned or un-tinned, copper conductor.
External generator grounding shall comply with the following:
• Bonding to the generator chassis shall be done in accordance with the manufacturer's requirements.
68P81089E50-B 9/1/05 4-59