standards and guidelines for communication sites - Radio And ...

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES MINIMUM SITE GROUNDING (EARTHING) REQUIREMENTS
2.4 m
(8 FT)
FIGURE 4-31 PARALLEL GROUND ROD INSTALLATION
EXOTHERMIC WELDS OR
IRREVERSIBLE HIGH
COMPRESSION FITTINGS
NOTE: It is recommended to use two grounding electrodes as the minimum installation, even if 25 ohms is
achieved with a single grounding electrode.
• Installation of a small ground ring (Figure 4-64 on page 4-89).
• Installation of an electrolytic ground rod.
At an existing building, the AC power system grounding electrode system will typically serve
adequately as the communications Type “A” grounding electrode system. A supplemental Type “A”
grounding electrode system may need to be installed if the site has an RF transmission line (or other
communications cables) entry point at a different location than the AC power utilities entrance. If a
supplemental Type “A” grounding electrode system is installed, it shall be bonded to any other
grounding electrode system at the site. See “Common Grounding (Earthing)” on page 4-5. For an
example of bonding a supplemental grounding electrode system to an existing AC power service
grounding electrode system, see Figure 4-54 on page 4-77 and Figure 4-64 on page 4-89.
NOTE: A single 2.4 m × 15.9 mm (8 ft. × 0.625 in.) ground rod requires a soil resistivity of approximately
6,250 ohm-cm or less throughout the year in order to achieve a resistance value of 25 ohms; a 3 m ×
15.9 mm (10 ft. × 0.625 in.) ground rod would require 7,500 ohm-cm; a 4.9 m × 15.9 mm (16 ft. × 0.625
in.) ground rod would require 11,200 ohm-cm; and a 6.1 m × 15.9 mm (20 ft. × 0.625 in.) ground rod
would require 13,600 ohm-cm. See Chapter , “Soil Resistivity Measurements,” for additional
information.
68P81089E50-B 9/1/05 4-49
2.4 m
(8 FT)