For 3/4" diameter electrical metallic tubing conduit that is 18" long, how many square inches can be used for conductor fill?

To determine the allowable conductor fill area for a 3/4" diameter electrical metallic tubing (EMT) conduit that is 18" long, we utilize the National Electrical Code (NEC) guidelines for conduit fill calculations. The NEC provides a specific set of formulas that allow us to calculate the fill area based on the interior diameter of the conduit.

The interior diameter of a 3/4" EMT is generally around 0.822 inches. To find the area full of conductor space, we use the formula for the area of a circle, which is A = πr². The radius (r) is half of the diameter, so in this case, the radius is approximately 0.411 inches.

Calculating the area gives us:

A = π(0.411)² ≈ 0.531 square inches (this is the total area of the conduit).

However, according to NEC standards, for conductor fill calculations, you take a percentage of the total area depending on how many conductors are occupying the conduit. For one conductor, the fill allowed is typically 53% of the total area:

Fill Area = 0.531 square inches × 0.53 ≈ 0.282 square inches