Conduit capacity: using two cables, what is the permitted conduit fill percentage?

• A. 60%
• B. 40%
• C. 53%
• D. 31%

Answer: (D)

Conduit fill is about how much of the conduit’s cross-sectional area can be occupied by conductors. The NEC sets fill limits based on the number and size of conductors inside a raceway to ensure there’s enough space for pulling the wires and for heat dissipation. When you run two cables in a conduit, the combined cross-sectional area of all conductors (plus any grounds) approaches the limit for that configuration, so the allowed fill is relatively small. For two cables, the permissible fill ends up at about 31%, which is why that option is correct. The larger percentages would exceed what’s allowed for this setup, making pulling difficult and increasing heat buildup.