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Wednesday, November 18, 1998
Question:
What is the minimum trade size, schedule 80 PVC, conduit that may be used for a run of three 4/0, three 1/0, one 2/0, one #2 all THWN and one 1/0 bare?
A
Answer:
Go to Chapter 9, Table 5, Dimensions of Insulated Conductors and Fixture Wires, to find the individual INSULATED conductor sizes and to Chapter 9, Table 8, Conductor Properties to find the individual BARE conductor areas in square inches. Tabulate the conductors similar to the following chart.
4/0 THWN = 0.3237 Sq. In. X three conductors = 0.9711 Sq. In
1/0 THWN = 0.1855 Sq. In. X three conductors = 0.5565 Sq. In
2/0 THWN = 0.2223 Sq. In. X one conductor = 0.2223 Sq. In
#2 THWN = 0.1158 Sq. In. X one conductor = 0.1158 Sq. In
1/0 Bare = 0.109 Sq. In. X one conductor = 0.109 Sq. In
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1.9747 Sq. In
Looking in Chapter 9, Table 4, Dimensions and Percent Area of Conduit and Tubing, find the portion for Rigid PVC Conduit, Schedule 80, look in the column for Over 2 Wires 40% Sq. In., find where 1.9747 square inches falls between, and choose the larger conduit. In this case it falls between 2 1/2 and 3 inch diameter so you would be required to use 3 inch schedule 80 as the smallest size conduit for this run.