3.5
DUCT LINES
**************************************************************************
NOTE: Communication lines run elsewhere will be
provided with the type of wall thickness that is in
accordance with the appropriate communication
agency's policy. Electrical metallic tubing will
not be installed underground or encased in concrete.
**************************************************************************
[Duct lines shall be concrete-encased, thin-wall type.] [Duct lines shall
be non-encased direct-burial, thick-wall type.] [Duct lines shall be
concrete-encased, thin-wall type for duct lines between manholes and for
other medium-voltage lines. Low-voltage lines run elsewhere may be
non-encased direct-burial, thick-wall type.] [Communication lines run
elsewhere may be direct-burial, thick-wall type.]
3.5.1
Requirements
Numbers and sizes of ducts shall be as indicated. Duct lines shall be laid
with a minimum slope of 100 mm per 30 m 4 inches per 100 feet. Depending
on the contour of the finished grade, the high point may be at a terminal,
a manhole, a handhold, or between manholes or handholes. Manufactured 90
degree duct bends may be used only for pole or equipment risers, unless
specifically indicated as acceptable. The minimum manufactured bend radius
shall be 450 mm 18 inches for ducts of less than 78 mm 3 inches diameter,
and 900 mm 36 inches for ducts 78 mm 3 inches or greater in diameter.
Otherwise, long sweep bends having a minimum radius of 7.6 m 25 feet shall
be used for a change of direction of more than 5 degrees, either
horizontally or vertically. Both curved and straight sections may be used
to form long sweep bends as required, but the maximum curve shall be 30
degrees and manufactured bends shall be used. Ducts shall be provided with
end bells when duct lines terminate in manholes or handholes. Duct line
markers shall be provided as indicated at the ends of long duct line
stubouts or for other ducts whose locations are indeterminate because of
duct curvature or terminations at completely below-grade structures. In
lieu of markers, a 0.127 mm 5 mil brightly colored plastic tape not less
than 76.2 mm 3 inches in width and suitably inscribed at not more than 3.0
m 10 feet on centers with a continuous metallic backing and a
corrosion-resistant 0.025 mm 1 mil metallic foil core to permit easy
location of the duct line, shall be placed approximately 300 mm 12 inches
below finished grade levels of such lines.
3.5.2
Treatment
Ducts shall be kept clean of concrete, dirt, or foreign substances during
construction. Field cuts requiring tapers shall be made with proper tools
and match factory tapers. After a duct line is completed, a standard
flexible mandrel shall be used for cleaning followed by a brush with stiff
bristles. Mandrels shall be at least 300 mm 12 inches long and shall have
diameters 6.2 mm 1/4 inch less than the inside diameter of the duct being
cleaned. Pneumatic rodding may be used to draw in lead wires. A coupling
recommended by the duct manufacturer shall be used when an existing duct is
connected to a duct of different material or shape. Ducts shall be stored
to avoid warping and deterioration with ends sufficiently plugged to
prevent entry of water or solid substances. Ducts shall be thoroughly
cleaned before being laid. Plastic ducts shall be stored on a flat surface
and protected from the direct rays of the sun.
SECTION 16526A
Page 34
Previous Page
