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

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES COMMON GROUNDING (EARTHING)
Communications facilities located at elevations significantly above the average elevation of the
surrounding terrain (such as hilltops, fire towers, airport control towers, and high-rise buildings) shall
be considered exposed to lightning regardless of thunderstorm activity and soil resistivity. (ANSI
T1.313-2003, section 5.1.1.)
Communications facilities with a tower shall be considered as exposed, regardless of thunderstorm
activity and soil resistivity. By their very construction, radio antennas/towers are considered exposed to
the possible damaging effects of lightning. Tall structures, such as towers, buildings and antenna masts,
provide a favorable discharge point for lightning strokes. (ANSI T1.313-2003, section 5.2.3.)
Some communications facilities may be classified as unexposed if the building and tower are within the
zone of protection of a higher structure. Only a qualified engineer should determine if the
communications facility is unexposed. The following standards can be used by the engineer to help
determine if the communications facility is unexposed: BS 6651:1999, IEC 61024-1-2, NFPA 780-
2004, or other applicable standard in effect and recognized by the local authority having jurisdiction.
4.3 COMMON GROUNDING (EARTHING)
At a communications site, there shall be only one grounding (earthing) electrode system. For example,
the AC power system ground, communications tower ground, lightning protection system ground,
telephone system ground, exposed structural building steel, underground metallic piping that enters the
facility, and any other existing grounding electrode system shall be bonded together to form a single
grounding electrode system (ANSI T1.313-2003; ANSI T1.333-2001; ANSI T1.334-2002; IEC 61024-
1-2, section 2.4.4; IEEE STD 1100-1999; NFPA 70-2005, Articles 250.58, 250.104, 250.106, 800.100,
810.21, and 820.100; and NFPA 780-2004, Section 4.14).
All grounding media in or on a structure shall be interconnected to provide a common ground potential.
This shall include, but is not limited to, the AC power system ground, communications tower ground,
lightning protection system ground, telephone system ground, exposed structural building steel, and
underground metallic piping systems. Underground metallic piping systems typically include water
service, well castings located within 7.6 m (25 ft.) of the structure, gas piping, underground conduits,
underground liquefied petroleum gas piping systems, and so on. Interconnection to a gas line shall be
made on the customer's side of the meter (NFPA 780-2004, Section 4.14.1.3).
68P81089E50-B 9/1/05 4-5