June 10, 2002
rating for the insulation temperature rating. The selected conductor size usually
depends on the following factors:
Voltage drop and regulation.
Temperature rise based on the insulation rating.
Ability to withstand short circuit heating.
Allowance for future load growth.
NEC Article 310.10 (2002 Edition) prohibits applying conductors in a manner
that will exceed the temperature rating for its insulation. Ensure an acceptable
temperature rating as follows:
Determine the current required by the loads.
Select the conductor size in accordance with NEC Article 310.15 (2002
Edition) for a given temperature rating.
Size cables with conductors rated for the next higher temperature. For
example, a circuit sized for a 75 °C (167 °F) insulated conductor would have a 90 °C
(194 °F)-rated insulation actually installed.
Refer to paragraph 6-2.13 for the minimum rating requirements.
All conductors must be copper, except aluminum conductors of equivalent
ampacity can be used instead o f copper for #4 American wire gauge (AWG) and larger
Select power conductor insulation suitable for the installation and conforming
to NEC requirements for each application. Select heat-resistant insulation for
conductors #6 AWG and larger.
Ensure feeders have an ampacity adequate for the loads to be served. Base
demand factors applicable to feeder loads upon the nature of the individual loads and
their use characteristics. Select demand factors in accordance with NEC Article 220
Rate branch circuits for a minimum of 20 amperes, except where lesser
ratings are required for specific applications. Branch circuit conductors, including power
and lighting applications, will in no case be less than #12 AWG copper. Although the