Single cable conduit fill maximum?

• A. 60%
• B. 40%
• C. 53%
• D. 31%

Answer: (C)

Conduit fill is about how much space the conductors can occupy inside a raceway. The NEC assigns a percent of the raceway’s inner cross-sectional area that can be filled by conductors. For a single cable in a conduit, the allowable fill is 53%. This higher allowance recognizes that a single cable has less packing and easier pulling compared to multiple conductors, which require more space for heat dissipation and movement.

If there were more than one conductor in the conduit, the limit drops to 40% to leave room for heat and ease of installation. The other percentages shown in the options correspond to different scenarios or conduit types, but for a single cable in a conduit, 53% is the applicable maximum.