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 MIL-HDBK-1012/3
reason for the application of grounding principles is to reduce
the effect of EMI and radio frequency interference (RFI).
NFPA 70, Section 800, EIA/TIA 569, BICSI Manual, Chapter 6,
FM11-490-9, MIL-HDBK-232, and MIL-HDBK-419, Grounding, Bonding,
and Shielding for Electronic Equipments and Facilities
Applications delineate the methodologies and requirements for
grounding of cable, conduit, tray, cabinets, and the building
structure. Extensive requirements are associated with developing
a facility ground system. The RCDD, while not usually required
to develop the detailed building ground system design, should be
well versed in the requirements of the referenced guidance
instructions and be prepared to offer assistance to ensure the
most effective communications grounding system is made available.
As discussed in par. 1.9.1, conductive cables entering a building
must have their shields grounded and be provided fused
protection, or be connected via an insulated joint, as close to
the service entrance as possible. This is generally accomplished
through the use of protectors as qualified by UL 497, Safety
Protectors for Paired Conductor Communication Circuits (primary),
and UL 497A, Safety Secondary Protectors for Communication
Circuits (secondary). Equipment cabinets, trays, conduit, duct,
etc., shall be bonded together with ground leads connected
directly to the building ground or the electrical panel ground,
whichever is closer. Connection via a 6 AWG wire is recommended.
Bonding shall be accomplished using approved bonding methods for
the application. It is recommended that copper buss be provided
in equipment cabinets and power panels to facilitate the
grounding and bonding of telecommunication equipment and cables.
In manholes, splice cases, and other metal items are to be bonded
to a ground rod driven a minimum 6 ft. into the ground. In areas
where cable may be exposed to lightning strike, particularly
aerial cable, a separate lightning rod with independent ground
pathway will be installed and located at least 2 m (6 ft.) from
the cable or cable entry point to the building.
The transfer rate, or operating speed, of
telecommunication accelerates with each passing year. As these
data rates increase, they become more susceptible to EMI and RFI.
To help reduce the effect of EMI and RFI, it is recommended that
exposed cables be specified to include shielding and a drain
wire. An exposed cable is defined as a cable which may be
subjected to lightning, power crosses, power induction, or
differences in ground potential. A cable shield is a metallic
covering of an insulated conductor, cable core, or group of
conductors within a cable core. A drain wire is a non-insulated
wire located within a cable sheath and adjacent to the shield or
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