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

GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING)
NOTE: Stainless steel ground rods shall be formed of an austenitic stainless steel of the 18 percent chromium, 8
percent nickel type (UL 467-2004, section 9.2.6).
• Ground rods shall have a minimum length of 2.4 m (8 ft.) (ANSI T1.313-2003, section 10.3.1,
ANSI T1.334-2002, section 5.3.2, NFPA 70-2005, Article 250.52, and UL 467-2004). For areas
highly prone to lightning, and/or military installations, longer rods, such as 3 m (10 ft.), should be
considered for the minimum length (MIL-HDBK-419A and MIL-STD-188-124B).
• Ground rods shall have a minimum diameter of 15.9 mm (0.625 in.) (ANSI T1.313-2003, section
10.3.1 and ANSI T1.334-2002, section 5.3.2), unless otherwise allowed by the UL listing of the
ground rod (UL 467). See NFPA 70-2005, Article 250.52 for additional information.
• Ground rods shall be free of paint or other nonconductive coatings (NFPA 70-2005, Article 250.53
and NFPA 780-2004, section 4.13.2).
4.4.1.2.2 GROUND ROD INSTALLATION
• Where practical, ground rods shall be buried below permanent moisture level (MIL-HDBK-419A
and NFPA 70-2005, Article 250.53).
• Where practical, ground rods shall penetrate below the frost line (MIL-HDBK-419A).
• Ground rods longer than the minimum required 2.4 m (8 ft.) may be required to maintain contact
with permanently moist, unfrozen soil (MIL-HDBK-419A).
• When part of a ground ring system, the upper end of the ground rods shall be buried to the depth of
the ground ring, typically 762 mm (30 in.) minimum below finished grade. The upper end of the
ground rods should be buried to the same depth as the ground ring to allow for easy bonding to the
ground ring. (See “External Building and Tower Ground Ring” on page 4-22.)
• When not part of a ground ring system, such as in a Type A site, the entire length of the rod shall be
in contact with soil (NFPA 70-2005, Article 250.53). It is recommended to install the ground rods
so the upper end of the rod is buried to a minimum depth of 610 mm (24 in.) below the surface of
the earth (NFPA 780-2004, section 4.13.2.3). See Figure 4-8 for typical single ground rod
installations.
4-12 68P81089E50-B 9/1/05