This document provides guidelines for grounding and lightning protection of communications antenna support structures. It specifies that antenna towers should be bonded to conductive equipment and structures and to a suitable grounding electrode. For towers under 75 feet located in low risk areas handling non-critical data, the steel reinforced concrete foundation can be used as the grounding electrode. For other systems, a grounding counterpoise of at least 4 ground rods spaced around the tower connected by insulated conductors should be installed. All equipment should be bonded to this grounding system and testing should confirm a resistance to earth of less than 5 ohms.

1. Engineering Standards
Standard
6020
Page
1 of 3
TRANSREDES GUIDELINEFOR GROUNDING Issue Date
AND LIGHTNINGPROTECTION OF 4/98
ANTENNA SUPPORT STRUCTURE Rev. No.
Date
4/98
* Indicates revised paragraph, this Rev. No.
1. SCOPE
This standard provides design guidelines for grounding and lightning surge protection of communications system
antenna support structures (towers) where installed at Company facilities.
2. CODES AND STANDARDS
Lightning Protection Institute Code, LPI-175
United Laboratories, Master Label for Lightning Protection, UL96A
National Fire Protection Association (NFPA)
3. GENERAL
Communication system antenna towers, because of their height, are likely to attract lightning strikes which elevate
voltages on all conductive elements connected to the structure. Properly designed and installed surge protection
and grounding systems can adequately protect even the most delicate electronic communication systems from
damage from such lightning strikes. If all equipment, buildings and utility grounds are electrically bonded to a
common grounding electrode with sufficient capacity to carry the surge current to earth, a lightning strike or other
surge will cause all systemcomponents to rise and fall with the surge potential at the same rate. If the surge potential
on all equipment rises and falls at the same rate and the surge current is safely drained away, equipment damage due
to arcing and excessive current should not occur.
3.1 All permanently installed, stationary antenna towers should be bonded to all conductive equipment and
structure in the vicinity and to a suitable ground electrode. If the antenna tower is located at a facility
having an electrical grounding system, the tower grounding electrode should be bonded to the facility
electrical grounding system.
3.2 The tower grounding electrode should function as a single electrode. The design should avoid connection
of extraneous grounding electrodes to the communications grounding system in a manner that creates
alternate paths to ground.
3.3 The design of the grounding electrode should be based on economics considering the probability of
lightning strikes on the tower, the criticality of service of the communications system and the cost of
replacement or repair of potential damage to the equipment. In addition to the following guidelines, the
appropriate technical supervisors and specialists responsible for corrosion control and communications at
the field operating level should be consulted for recommendations relative to grounding electrode design or
surge related problems at existing communications facilities.
3.3.1 The steel reinforced concrete foundation of the antenna tower should be used as the tower
grounding electrode for communication systeminstallations meeting all of the following criteria.
a. Tower height is 75 feet or less.
b. Facility is not located in a high risk area for lightning strikes such as south-central Florida
or as demonstrated by experience on an existing or other similar installations in the local
area.

2. Engineering Standards
Standard
6020
Page
2 of 3
TRANSREDES GUIDELINEFOR GROUNDING Issue Date
AND LIGHTNINGPROTECTION OF 4/98
ANTENNA SUPPORT STRUCTURE Rev. No.
Date
4/98
* Indicates revised paragraph, this Rev. No.
c. The communications system does not handle information that, if temporarily lost, would
have potential serious financial or safety impact. Data from multiple operating facilities,
pipeline control signals and voice communications are examples of information that may
be considered to have such potential.
d. Soil resistivity at the site is not suspected or measured to exceed 2000 ohm-cm.
3.3.2 For communication systems not meeting the criteria in Section 3.3.1, a tower grounding
counterpoise should be installed.
4. DESIGN
4.1 For steel reinforced concrete foundation used as grounding electrodes, each tower anchor bolt should be
bonded to the steel reinforcement and all equipment and structural elements should be bonded to the tower.
If necessary to lower the resistance to earth of this design, as determined by the post-installation test, one
or more ground rods may be driven around the foundation and bonded to the leg(s) of the tower in a manner
similar to the grounding counterpoise described in Section 4.2.
4.2 A tower grounding counterpoise should consist of a minimum of four ground rods spaced a minimumof 12
feet apart in a symmetrical pattern around the base of the tower and connected with bonding conductors to
forma loop. The loop should be connected and bonded to each leg of the tower.
4.2.1 Ground rods should be installed with the top of the rod a minimum of one foot below finished
grade.
4.2.2 All buried bonding conductors should be insulated and installed in trenches a minimumof one
foot deep.
4.2.3 If the antenna tower is supported by guys, every guy and guy anchor should be connected to
the tower grounding electrode or counterpoise. A separate bonding conductor should be
routed to each guy anchor but may be tapped for bonding to each guy cable terminated at the
guy anchor.
4.3 Antennas with a non-conductive exterior surface such as fiberglass that are side-mounted on the tower
should be protected from a direct lightning strike by an air terminal installed on foot above the top or the
antenna and extending horizontally one foot beyond the top of the antenna.
4.4 All buried metallic components shall be cathodically protected by bonding to existing facilities or a separate
rectifier systemor anodes.

3. Engineering Standards
Standard
6020
Page
3 of 3
TRANSREDES GUIDELINEFOR GROUNDING Issue Date
AND LIGHTNINGPROTECTION OF 4/98
ANTENNA SUPPORT STRUCTURE Rev. No.
Date
4/98
* Indicates revised paragraph, this Rev. No.
5. MATERIALS
5.1 Bonding conductors should be heavy gauge, stranded, lead-coated, braided copper specifically
manufactured for conducting surge currents created by lightning. For example, Thompson Lightning
Protection Company, catalog #48 is acceptable for this application. Conductors bonding communications
equipment cabinets and chassis to the grounding electrode may be #6 AWG, bare, solid copper provided
such conductors are bonded to a lead-coated, braided, copper conductor prior to leaving the cabinet or
building containing the equipment.
5.2 Ground rods should be stainless steel, zinc or zinc clad rods, 5/8" diameter, non-sectionalized and a minimum
of 10 feet long.
5.3 Fittings and attachments should be copper-bronze bodied and specifically manufactured for application in
lightning protection systems. Exposed connections should be bolted compression type. Buried
connections should be made using a fusible metal process such as Cadweld.
5.4 Air terminals should be stainless steel and 1/2" diameter minimum.
6. TESTING
Using the Direct or Two-terminal measurement method, resistance to earth should be measured between all
equipment bonded to the antenna tower ground electrode and a derived earth reference electrode placed not less
than 50 feet away from the tower ground electrode. The measured resistance should be less than 5 ohms and shall
not exceed 25 ohms.