When designing an underfloor duct system, which of the following would be the cross-sectional area of the duct serving each 100 square feet of floor space with 3 cables to each of the work areas.

3 square inches exceeds the NEC-specified cross-sectional area requirement and does not correspond to the standard formula for 3 cables serving 100 square feet of floor space.

4 square inches is more than four times the required cross-sectional area specified by NEC Article 390 for this cable density and floor area combination.

Per NEC Article 390 (Underfloor Raceways), the cross-sectional area of a duct serving each 100 square feet of floor space with 3 cables to each work area is 1 square inch. This sizing standard ensures proper fill ratios and code-compliant cable management within underfloor raceway systems. The 1 square inch per 100 square feet per 3-cable configuration is the code-mandated calculation for these installations.

5 square inches significantly exceeds the 1 square inch NEC requirement, making it non-compliant for an underfloor duct serving 100 square feet with 3 cables.