Which 2 Inch Raceway Has the Largest Cross Sectional Area?

Intermediate metal conduit wins. At the 2 inch trade size, IMC has an internal cross sectional area of 3.630 square inches, which is the largest of any raceway listed in NEC 2023 Chapter 9, Table 4 at that size. It is a favorite exam question because most people assume rigid metal conduit is the biggest, and it is not.

The 2 inch lineup from Table 4

Here is the ranking at 2 inch trade size, total area first and the 40 percent fill in parentheses. IMC leads at 3.630 square inches (1.452). Rigid metal conduit follows at 3.408 square inches (1.363). EMT and liquidtight flexible metal conduit come in at 3.356 square inches (1.342). Flexible metal conduit is 3.269 square inches (1.307). PVC Schedule 40 and ENT are 3.291 square inches (1.316). PVC Schedule 80 is the smallest of the common ones at 2.874 square inches (1.150).

The reason IMC beats RMC is wall thickness. Both are threaded steel conduits with the same outside diameter at a given trade size, because they have to accept the same fittings and couplings. IMC is manufactured with a thinner wall using a higher strength steel, so all that saved wall thickness becomes interior space. That is also why IMC weighs roughly a third less than RMC per foot, which matters on a rack of overhead runs.

Where this actually shows up on a job

The margin is real but small. IMC gives you 1.452 square inches of usable fill versus 1.363 for RMC, about 6.5 percent more room. That is occasionally the difference between fitting one more conductor in an existing raceway and having to add a pipe. Six 250 kcmil THHN at 0.3970 square inches each is 2.382, which exceeds both. Three 500 kcmil THHN at 0.7073 each is 2.122, which also exceeds both. Four 4/0 THHN at 0.3237 is 1.295, which fits every one of the metal options and PVC 40 but is too tight for PVC 80 at 1.150.

PVC Schedule 80 is the one to watch on any job with exposed conduit subject to physical damage, since 352.10(F) requires Schedule 80 where the raceway is subject to damage, and that thicker wall costs you almost 13 percent of the interior compared to Schedule 40. Designers who spec a conduit size from a Schedule 40 fill table and then get Schedule 80 in the field are the source of a lot of change orders.

Two habits keep you out of trouble. First, always read the 40 percent column straight from Table 4 rather than multiplying, because Table 4 has already done the arithmetic and includes the correct internal diameters. Second, always confirm which raceway type you are actually installing before you size it, since Table 4 has a separate block for every single raceway article and the numbers are close enough to grab the wrong row without noticing.