2.4
CABLES
**************************************************************************
NOTE: Justify selection of copper or aluminum,
based upon an analysis using life-cycle,
environmental, and cost factors. Refer to TM
5-811-1/AF AFJMAN 32-1080 for guidance regarding
cables.
**************************************************************************
Cables shall be single conductor type unless otherwise indicated.
2.4.1
Medium-Voltage Cables
**************************************************************************
NOTE: Medium voltage cables are complex and
sophisticated products that can be manufactured to
have very specific properties for the installed
environment. The two most commonly
produced/specified medium voltage cables are Type MV
(as described in UL 1072) and underground
distribution ("UD/URD"), commonly used by electrical
utilities. Type MV is a type designation recognized
by NFPA 70 because it is UL listed. "UD/URD" is not
a recognized type designation because it is utilized
primarily by electrical utilities, who are not
governed by NFPA 70 and for whom a UL listed cable
adds unnecessary expense. Both type MV and "UD/URD"
can be specified for use in duct or direct buried.
Type MV cable are typically manufactured with copper
or aluminum conductors; an extruded semi-conductor
conductor shield; ethylene-propylene rubber (EPR) or
cross-linked polyethylene (XLP) insulation; an
insulation shield consisting of extruded
semi-conductor and metal tape; and a polyvinyl
chloride (PVC) jacket. "UD/URD" cables are
typically manufactured with copper or aluminum
conductors; an extruded semi-conductor conductor
shield; an insulation shield consisting of extruded
semi-conductor and metal tape, or extruded
semi-conductor with concentric-wound copper drain
wires; cross-linked polyethylene (XLP) insulation; a
concentric neutral; and a polyethylene jacket. A
cable can be made from almost any combination of
conductors, insulations, shields and jackets;
therefore, the designer needs to specify a cable
that meets the needs of the application. Utilize
either Type MV or "UD/URD" in ducts, keeping in mind
that the concentric neutral affects bending radius
and pulling tensions, therefore limiting the maximum
pull and distance between manholes. Utilize "UD"
for direct buried applications. Select full
ampacity concentric neutral for single-phase
applications and one-third ampacity for three-phase
applications.
**************************************************************************
SECTION 16375A
Page 19
Previous Page
