Quantcast Facility Ground System

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MIL-HDBK-419A
1.5 DESCRIPTION. The ground system serves three primary functions which are listed below. A good ground
system must receive periodic inspection and maintenance to retain its effectiveness. Continued or periodic
maintenance is aided through adequate design, choice of materials, and proper installation techniques to ensure
that ground subsystems resist deterioration or inadvertent destruction and thus require minimal repair to retain
their effectiveness throughout the life of the facility.
a .  Personnel safety. Personnel safety is provided by low-impedance grounding and bonding between
equipment, metallic objects, piping, and other conductive objects, so that currents due to faults or lightning do
not result in voltages sufficient to cause a shock hazard.
b .  Equipment and facility protection.Equipment and facility protection is provided by low-impedance
grounding and bonding between electrical services, protective devices, equipment, and other conductive objects,
so that faults or lightning currents do not result in hazardous voltages within the facility. Also, the proper
operation of overcurrent protective devices is frequently dependent upon low-impedance fault current paths.
c .  Electrical noise reduction. Electrical noise reduction is accomplished on communication circuits by
ensuring that (1) minimum voltage potentials exist between communications-electronics equipments, (2) the
impedance between signal ground points throughout the facility to earth is minimal, and (3) that interference
from noise sources is minimized.
1.5.1 Facility Ground System. All telecommunications and electronic facilities are inherently related to
earth by capacitive coupling, accidental contact, and intentional connection. Therefore, ground must be looked
at from a total system viewpoint, with various subsystems comprising the total facility ground system. The
facility ground system forms a direct path of known low impedance between earth and the various power,
communications, and other equipments that effectively extends in approximation of ground reference
throughout the facility. The facility ground system is composed of an earth electrode subsystem, lightning
protection subsystem, fault protection subsystem, and signal reference subsystem.
a .  Earth electrode subsystem. The earth electrode subsystem consists of a network of earth electrode
rods, plates, mats, or grids and their interconnecting conductors. The extensions into the building are used as
the principal ground point for connection to equipment ground subsystems serving the facility. G r o u n d
reference is established by electrodes in the earth at the site or installation. The earth electrode subsystem
includes the following: (1) a system of buried, driven rods interconnected with bare wire that normally form a
ring around the building; or (2) metallic pipe systems, i.e., water, gas, fuel, etc., that have no insulation joints;
or (3) a ground plane of horizontal buried wires. Metallic pipe systems shall not be used as the sole earth
electrode subsystem. Resistance to ground should be obtained from the appropriate authority if available or
determined by testing. For EMP considerations, see Chapter 10.
b .  Lightning protection subsystem. The lightning protection subsystem provides a nondestructive path
to ground for lightning energy contacting or induced in facility structures. To effectively protect a building,
mast, tower, or similar self-supporting objects from lightning damage, an air terminal (lightning rod) of
adequate mechanical strength and electrical conductivity to withstand the stroke impingement must be
provided. An air terminal will intercept the discharge to keep it from penetrating the nonconductive outer
coverings of the structure, and prevent it from passing through devices likely to be damaged or destroyed. A
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