How many cables fit in conduit — NEC Chapter 9 compliant
It depends on conduit size, cable diameter, and the number of conductors. Under NEC Chapter 9, a single cable may use up to 53% of the internal area, two cables are limited to 31%, and three or more cables share a 40% limit. Use the Max Cables tab to compute an exact count for your situation.
NEC Table 1 of Chapter 9 requires that when three or more conductors or cables occupy a raceway, their combined cross-sectional area must not exceed 40% of the conduit's internal area. This rule ensures adequate heat dissipation and allows room for installation.
First compute each cable's area: π × (diameter ÷ 2)². Multiply by the number of cables to get total cable area. Divide by the conduit's internal area and multiply by 100 to get the fill percentage. Compare against 53% (1 cable), 31% (2 cables), or 40% (3+ cables).