CHAPTER 3
EXAMPLES AND TABLES
COMMENTARY AT 310.14 INFORMATIONAL NOTE
The primary information in Tables 310.104(A) through Table 310.104(E) is the minimum required insulation
thickness for each insulation type and voltage level. Additional detailed wire classification information for
sizes 14 AWG through 2000 kcmil is available in standards and directories such as those published by
Underwriters Laboratories Inc.
Table 310.104(A) includes conductor applications and maximum operating temperatures. It also lists some
conductors that have dual ratings, such as Type XHHW, which is rated 90°C for dry and damp locations and
75°C for wet locations, and Type THW, which is rated 75°C for dry and wet locations and 90°C for special
applications within electric-discharge lighting equipment.
Types RHW-2, XHHW-2, and other types identified by the suffix “2” are rated 90°C for wet locations as well as
dry and damp locations.
Copper-clad aluminum conductors are drawn from a copper-clad aluminum rod with the copper
metallurgically bonded to an aluminum core. The copper forms a minimum of 10 percent of the crosssectional area of a solid conductor or of each strand of a stranded conductor. See the commentary following
310.106(B) for making electrical connections with different types of conductor material. A comparison of the
characteristics of copper, copper-clad aluminum, and aluminum conductors can be made from Commentary
Table 310.2.
Commentary Table 310.2 Conductor Characteristics
Characteristic
Density (lb/in.3)
Density (g/cm3)
Resistivity (ohms/CMF)
Resistivity microhm — CM
Conductivity (IACS %)
Weight % copper
Tensile K psi — hard
Tensile kg/mm2 — hard
Tensile K psi — annealed
Tensile kg/mm2 — annealed
Specific gravity
Copper
0.323
8.91
10.37
1.724
100
100
65.0
45.7
35.0
24.6
8.91
Copper-Clad Aluminum
0.121
3.34
16.08
2.673
61–63
26.8
30.0
21.1
17.0
12.0
3.34
Aluminum
0.098
2.71
16.78
2.790
61.0
—
27.0
19.0
17.0*
12.0
2.71
*Semiannealed
COMMENTARY AT 376.22
The requirements of 376.22(A) for the number of conductors are as follows:

All conductors count in determining wireway fill.

Total conductor fill must not exceed 20 percent of the wireway.
The conductor ampacity requirements of 376.22(B) are as follows:

Conductor ampacity is determined according to 310.15.

Where the quantity of current-carrying conductors does not exceed 30, the adjustment factors of
310.15(B)(3)(a) do not apply.

Where the quantity of current-carrying conductors does exceed 30, the adjustment factors of
310.15(B)(3)(a) only do apply. This includes any current-carrying neutrals.

Neutral conductors are determined to be current-carrying conductors according to 310.15(B)(5).

Signaling circuit conductors are not considered current-carrying conductors.

Conductors used only for motor-starting duty as limited by 376.22(B) are not considered currentcarrying conductors.
The following installation example consists of a wireway with 26 current-carrying conductors; therefore, the
adjustment factors of 310.15(B)(3)(a) do not apply.
Calculation Example
A wireway contains 26 conductors: ten 3/0 AWG XHHW-2, three 6 AWG THWN, three 8 AWG THHN, and ten
12 AWG THHN. Find the minimum standard size wireway required by Article 376.
Solution
Conductor Type and Size
Quantity
Total Area (in.2)
Individual Area* (in.2)
3/0 AWG, XHHW-2
10 ×
0.2642
=2.6420
6 AWG, THWN
3×
0.0507
= 0.1521
8 AWG, THHN
3×
0.0366
= 0.1098
12 AWG, THHN
10 ×
0.0133
= 0.1330
Total area occupied by conductors
Minimum wireway area required:
3.0369 𝑖𝑛.2 ÷ 20 % 𝑓𝑖𝑙𝑙 = 15.1845 𝑖𝑛.2
Minimum size square wireway required:
3.0369
15.1845 𝑖𝑛.2 = 3.9 𝑖𝑛. × 3.9 𝑖𝑛. 𝑜𝑟 4 𝑖𝑛. × 4 𝑖𝑛. wireway
*Individual area dimensions of conductors are from Chapter 9, Table 5.