Sizing Wireways – Both Nonmetallic and Metallic

Sizing Wireways

Sizing a wireway to hold a predetermined number of conductors is similar to sizing raceways.

First, determine the total area of the conductors in square inches. This is found by using Table 5 for insulated conductors, Table 5A for compact conductors, or Table 8 for bare conductors. Take the total area of these conductors, divide by 20% or multiply by 5, and take the square root to find the appropriate size wireway.

For example, what size of wireway is required for the following THNN conductors?

• Four 600 kcmil THNN conductors
• Four 400 kcmil THNN conductors
• Three 300 kcmil THNN conductors

See Table 5 to determine the area of each conductor.

600 kcmil THHN = 0.8676 sq in.
400 kcmil THHN = 0.5863 sq in.
300 kcmil THHN = 0.4608 sq in.

Next, Multiply the area by the number of conductors:

0.8676 sq in. × 4 = 3.4704 sq in.

0.5863 sq in. × 4 = 2.3452 sq in.

0.4608 sq in. x 3 = 1.3824 sq in.

Add the area of all the conductors: 3.4704 + 2.3452 + 1.3824 = 7.198 sq in.

Now, take the total area (7.198 sq. in) and divide it by 5, and take the square root it:

7.198 x 5 = 35.99 square root is: 5.99”

The next highest standard wireway size from 5.99” is 6” x 6”

Let’s Confirm: 6” x 6” is 36 Inches x 20% = 7.2 sq in. and as you saw above our conductors took up 7.198 sq. in. so the 6” x 6” wireway is perfect.

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