What is the minimum trade size Schedule 80 PVC that can be installed up a wooden pole that is 20 feet tall containing four 500 kcmil conductors and one 1/0 AWG ground, all THHN/THWN copper?

What is the minimum trade size Schedule 80 PVC that can be installed up a wooden pole that is 20 feet tall containing four 500 kcmil conductors and one 1/0 AWG ground, all THHN/THWN copper?

• A. 2 in.
• B. 2-1/2 in.
• C. 3 in.
• D. 3-1/2 in.

Answer: (D)

The main idea is conduit fill: the raceway must have enough interior space to hold all conductors with the allowed fill percentage, so you pick the smallest conduit that meets that requirement. First, convert each conductor to its cross‑sectional area in circular mils. Four 500 kcmil conductors have a combined area of 4 × 500,000 = 2,000,000 circular mils. The equipment grounding conductor (1/0 AWG) adds 105,000 circular mils. Total conductor area = 2,105,000 circular mils. For a conduit, the allowed fill for conductors is 40%. So the interior cross‑sectional area must be at least 2,105,000 / 0.40 ≈ 5,262,500 circular mils, which is about 4.13 square inches of interior cross‑section (since 1 in^2 ≈ 1,273,239 circular mils). Consulting Schedule 80 PVC conduit interior sizes, the 2-1/2 in size and the 3 in size do not provide at least 4.13 in^2 of interior area, but the 3-1/2 in size does. Therefore, the smallest Schedule 80 PVC conduit that can physically accommodate these five conductors with the 40% fill rule is the 3-1/2 in size.

The main idea is conduit fill: the raceway must have enough interior space to hold all conductors with the allowed fill percentage, so you pick the smallest conduit that meets that requirement.

First, convert each conductor to its cross‑sectional area in circular mils. Four 500 kcmil conductors have a combined area of 4 × 500,000 = 2,000,000 circular mils. The equipment grounding conductor (1/0 AWG) adds 105,000 circular mils. Total conductor area = 2,105,000 circular mils.

For a conduit, the allowed fill for conductors is 40%. So the interior cross‑sectional area must be at least 2,105,000 / 0.40 ≈ 5,262,500 circular mils, which is about 4.13 square inches of interior cross‑section (since 1 in^2 ≈ 1,273,239 circular mils).

Consulting Schedule 80 PVC conduit interior sizes, the 2-1/2 in size and the 3 in size do not provide at least 4.13 in^2 of interior area, but the 3-1/2 in size does. Therefore, the smallest Schedule 80 PVC conduit that can physically accommodate these five conductors with the 40% fill rule is the 3-1/2 in size.