Which unit does NEC table 314.16B use to express conductor volume?

• A. Cubic inches
• B. Cubic centimeters
• C. Cubic feet
• D. Square inches

Answer: (A)

Conduit fill is determined by the volume that conductors occupy inside a raceway. NEC table 314.16B expresses that conductor volume in cubic inches, so you can add up the total volume of all conductors and compare it to the raceway’s allowable volume, also in cubic inches. This unit is used because raceway interiors are sized in inches and the volumes involved are conveniently measured in cubic inches. Cubic centimeters would be awkward in the US practice, cubic feet would be too large for typical raceways, and square inches measure area, not volume, so they don’t represent the space the conductors take up.