The designer will verify local electrical
installation requirements to determine if new
grounding conductors and electrodes are required at
each messenger cable ground connection and will
select the first, or second, or both bracketed
entries as determined to be necessary.
Common lashing machines provide 1 turn per 380
linear mm (1 turn per 15 linear inches) in a single
pass, which is acceptable for locations where
loading due to weather conditions is moderate.
Other locations may require multiple passes with the
lashing machine.
Percent values stated below for messenger rated
breaking strength are based upon overload factors
that apply to Grade B construction. If the aerial
electrical distribution system construction is a
lesser grade (e.g., Grade C, Grade N, or not graded)
differing values will be provided by the designer in
accordance with NESC and actual requirements.
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Except as otherwise specified, poles and associated aerial hardware for an
overhead FO cable system shall be installed as specified in Section 16370A
ELECTRICAL DISTRIBUTION SYSTEM, AERIAL, as specified herein, and as shown.
a. A messenger system meeting the requirements of IEEE C2 to support
aerial cables shall be furnished and installed. The messenger system
shall include all messenger support and attachment hardware and
appurtenances needed to install the messenger. Messenger tension due
to combined ice and wind loading on the messenger with supported cables
shall not exceed 60 percent of the messenger rated breaking strength.
Messenger tension due to extreme wind loading on the messenger with
supported cables shall not exceed 80 percent of the messenger rated
breaking strength. Messenger support and attachment hardware shall
have rated strength not less than the messenger rated breaking
strength. All messenger support and attachment hardware and
appurtenances shall be sized to exceed the rated breaking strength of
the messenger cable. Messenger cables shall be galvanized zinc coated
steel or aluminum clad steel.
b. The messenger cables shall be grounded at all corners, dead ends, at
the entrance to each facility, and at intervals not exceeding 305
meters 1000 feet. [New grounding conductors and electrodes shall be
provided at each ground connection.] [Where grounding connections are
made in the vicinity of existing grounding conductors and electrodes,
the grounding connection may be made by a bolted or welded connection
to the existing grounding conductor.]
c. Aerial FO cables shall meet the horizontal, vertical and climbing
space clearances prescribed in IEEE C2 and those of the installation.
d. Transitions from aerial cable to underground cable shall be as
specified in paragraph CONNECTIONS BETWEEN AERIAL AND UNDERGROUND
SYSTEMS in Section 16370A ELECTRICAL DISTRIBUTION SYSTEM, AERIAL and as
shown.
SECTION 16768A
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