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Furnish and install a messenger cable system to support aerial cables.
Messengers shall be attached to poles with approved clamps with not less
than 15.9 mm 5/8 inch through bolts. Messenger cable tensioning shall not
exceed 30 percent of its rated breaking strength under 16 degrees C 60
degrees F conditions of no ice and no wind. The messenger cable shall be
stressed prior to lashing the cables to a tension higher than the final
tension. This will prestretch the cable and ensure that there are minimum
variations from the calculated values when the messenger is dead-ended
under its final tension and sag. Messengers shall be grounded and guyed at
all corners, dead-ends, entrances to each facility, and grounded at
intervals not exceeding 305 m 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.] Ground conductors shall
be soft drawn copper, having a current capacity of at least 20 percent of
that of the messenger to which it is connected. Ground conductors shall
not be smaller than No. 6 AWG. The ground conductor shall be connected to
a copper or copper-clad steel ground rod not less than 19.1 mm 3/4 inch in
diameter, and length shall be as needed to achieve the specified ground
resistance. After installation is completed, the top of the ground rod
shall be approximately 300 mm 1 foot below finished grade. The ground
conductor shall be protected by half-round wood, plastic, or fiber molding
from the ground to a point at least 2.4 m 8 feet above the ground. Ground
resistance shall be measured in normally dry conditions, not less than 48
hours after a rainfall, and the total ground resistance shall not exceed
[25] [_____] ohms.
b. Transitions from Aerial Cable to Underground: Transitions from
aerial cable to underground cable shall be as specified (and consistent
with those specified) in CONNECTIONS BETWEEN AERIAL AND UNDERGROUND
SYSTEMS in Section 16370A ELECTRICAL DISTRIBUTION SYSTEM, AERIAL.
c. Aerial Cable Splices: All splices in aerial cable shall be within 1
m 3 feet of a pole and placed inside a watertight enclosure. Drip
loops shall be formed at the cable entrance to the enclosure. Lashing
clamps shall be placed within 300 mm 12 inches of the enclosure.
d. Lashing Wire: Lashing wire shall be wound tightly around both the
communication cable and the messenger cable by machine methods. The
lashing wire shall have a minimum of 1 turn per 380 linear mm 15 linear
inches and not less than the number of turns per linear mm linear foot
that is recommended by the cable manufacturer for the distance between
cable support points and the combined ice and wind loading and extreme
wind loading specified or normally encountered for the installed
location. Lashing clamps shall be placed at all poles and splices.
e. Stress Loops: Loops shall be formed in the aerial DTS cable at all
points of connection and at all poles to prevent damage from thermal
stress and wind loading. The DTS cable shall be protected from chafing
and physical damage with the use of spiral cut tubing and PVC tape, or
plastic sleeves. The ground clearance of installed cabling shall be as
shown.
f. Enclosure Penetrations: All enclosure penetrations shall be from
the bottom and shall be sealed with rubber silicone sealant to preclude
the entry of water.
SECTION 16792A
Page 17
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