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

MINIMUM SITE GROUNDING (EARTHING) REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING)
GROUNDING CONDUCTOR
3 m
(10 ft.)
610 mm
(2 ft)
2.4 m
(8 ft.)
FIGURE 4-32 TYPICAL SINGLE GROUNDING ELECTRODE INSTALLATION
4.7.6 TOWER GROUNDING (EARTHING)
An external grounding (earthing) electrode system for a communications tower is required to disperse
lightning energy to earth before it is able to enter the associated communications structure (or
enclosure). Although is impossible to prevent all lightning energy from entering the communications
structure (or enclosure), the majority of the lightning energy can be controlled and diverted to earth
(ANSI T1.313-2003 and ANSI T1.334-2002). Antenna masts and metal support structures shall be
grounded (NFPA 70-2005, Article 810.15).
IMPORTANT: For towers installed at high lightning prone geographical areas or sites normally
occupied (such as 911 dispatch centers), radial grounding conductors should be employed to improve
equalization of the grounding electrode system (ANSI T1.334-2002, section 5.4). See “Radial
(Counterpoise) Grounding Conductors” on page 4-24. This is recommended even if the grounding
electrode system resistance requirement is met without the use of radial grounding conductors.
Towers can be classified into three basic categories (ANSI T1.334-2002, section 6.3):
• Self-Supporting Towers (including monopoles)
• Guyed Towers
• Wooden Structures (poles)
GROUNDING CONDUCTOR
RECOMMENDED DEPTH MINIMUM DEPTH
TOP OF ROD JUST
BELOW SOIL
SURFACE
4-50 68P81089E50-B 9/1/05
2.4 m
(8 ft.)