Cooper Bussmann CT02MAN - Manual (Page 7)

CABLE TRAY WIRING SYSTEM
COST SAVINGS
Usually, the initial capital cost is the major factor
in selecting a project's wiring system when an
evaluation is made comparing cable tray wiring
systems and conduit wiring systems. Such an
evaluation often covers just the conductors, material,
and installation labor costs. The results of these
initial cost evaluations usually show that the installed
cable tray wiring system will cost 10 to 60 percent
less than an equivalent conduit wiring system. The
amount of cost savings depends on the complexity
and size of the installation.
There are other savings in addition to the initial
installation cost savings for cable tray wiring systems
over conduit wiring systems. They include reduced
engineering costs, reduced maintenance costs,
reduced expansion costs, reduced production losses
due to power outages, reduced environmental
problems due to continuity of power and reduced
data handling system costs due to the continuity of
power. The magnitudes of many of these costs
savings are difficult to determine until the condition
exists which makes them real instead of potential
cost savings.
DESIGN COST SAVINGS
• Most projects are roughly defined at the start of
design. For projects that are not 100 percent
defined before design start, the cost of and time
used in coping with continuous changes during the
engineering and drafting design phases will be
substantially less for cable tray wiring systems than
for conduit wiring systems. A small amount of
engineering is required to change the width of a
cable tray to gain additional wiring space capacity.
Change is a complex problem when conduit banks
are involved.
• The final drawings for a cable tray wiring
system may be completed and sent out for bid or
construction more quickly than for a conduit wiring
system. Cable tray simplifies the wiring system
design process and reduces the number of details.
• Cable tray wiring systems are well suited for
computer aided design drawings. A spread sheet
based wiring management program may be used to
control the cable fills in the cable tray. While such a
system may also be used for controlling conduit fill,
large numbers of individual conduits must be
monitored. For an equal capacity wiring system,
only a few cable tray runs would have to be
monitored.
• Dedicated cable tray installation zones alert
other engineering disciplines to avoid designs that
will produce equipment and material installation
conflicts in these areas. As more circuits are added,
the cable tray installation zone will increase only a
few inches; the space required for the additional
conduits needed would be much greater.
• The fact that a cable can easily enter and
exit cable tray anywhere along its route,
allows for some unique opportunities that provide
highly flexible designs.
• Fewer supports have to be designed and less
coordination is required between the design
disciplines for the cable tray supports compared to
conduit supports.
MATERIAL COST SAVINGS
• Excluding conductors, the cost of the cable
trays, supports, and miscellaneous materials will
provide a savings of up to 80% as compared to the
cost of the conduits, supports, pull boxes, and
miscellaneous materials. An 18 inch wide cable tray
has an allowable fill area of 21 square inches. It
would take 7 - 3 inch conduits to obtain this
allowable fill area (7 x 2.95 square inches = 20.65
square inches).
• The cost of 600 volt insulated multiconductor
cables listed for use in cable tray is greater than the
cost of 600 volt insulated individual conductors used
in conduit. The cost differential depends on the
insulation systems, jacket materials and cable
construction.
• For some electrical loads, parallel conductors
are installed in conduit and the conductors must be
derated, requiring larger conductors to make up for
the deration. If these circuits were installed in cable
tray, the conductor sizes would not need to be
increased since the parallel conductor derating
factors do not apply to three conductor or single
conductor cables in cable tray.
• Typical 300 volt insulated multiconductor
instrumentation tray cables (ITC) and power limited
tray cables (PLTC) cost the same for both cable tray
and conduit wiring systems. This applies for
instrumentation circuits, low level analog and digital
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Cable Tray Manual Cooper B-Line, Inc