UFC 3 -520-01
June 10, 2002
Base branch circuit and feeder sizes upon temperature rating requirements
established by the NEC. The conductor must be sized so that termination temperatures
do not exceed 60 C (140 F) for conductors smaller than 100 amperes or #1 AW G, and
75 C (167 F) for conductors larger than 100 amperes or 1/0 AWG. This means that
the 60 C (140 F) column of NEC Table 310 .16 (2002 Edition) should be used for
conductor sizing of circuits 100 amperes and smaller, and the 75 C (167 F) column of
NEC Table 310.16 (2002 Edition) should be used for conductors larger than 100
Terminate all conductors properly in accordance with the manufacturer's
recommended procedures. Ensure that the proper crimping tools are available for each
type of termination, as applicable.
The use of splices is discouraged unless required for a specific application. If
splices are used, splice or join conductors with splicing devices suitable for the use.
Cover all splices and joints and the free e nds of conductors with an insulation equivalent
to that of 150 percent of the conductors or with an insulating device suitable for the
purpose. Do not intermix conductors of dissimilar metals where physical contact occurs
between the dissimilar metals (such as copper and aluminum) unless the device is
identified for the purpose and conditions of use. Conductors in conduit or raceway
systems must be continuous from outlet to outlet. If necessary, splices are permitted for
the service entrance conductors i n accordance with NEC Article 230.46 (2002 Edition).
Install splices only in areas such as boxes and panels designed to allow splices. The
above criteria regarding splices do not prohibit the use of wire nuts or other connection
devices to connect conduc tors to end use devices.
Nonmetallic sheathed cable with ground conductor can be used for branch
circuits in wood frame buildings or in stud walls of concrete, masonry, or metal
buildings, subject to the limitations specified by NEC Article 334 (2002 Edition) . Protect
the cable from physical damage where necessary by one or more of the methods
allowed by NEC Article 334 (2002 Edition) .
SIZING WIRING SYSTEMS FOR ENERGY SAVINGS .
Paragraph 6-2 provides the minimum required design criteria for conductor
sizing. Although not a specific design requirement, every design should be evaluated
for the energy savings possible by installing conductors of one size larger than required
by the NEC. By increasing the wire size, reduced power losses offset the wire cost and
often show a payback within a relatively short time. Also, the increased wire size
improves the system flexibility to accommodate future design changes. In summary,
increasing the wire size to one size larger than required by the NE C produces the
Energy savings will be realized due to lower heating losses in the larger conductors.
Less heat will be generated by the wiring system.