In a new conduit with four wires, the total cross-sectional area of conductors (not lead-covered) shall not exceed what percentage of the conduit cross-sectional area?

• A. 31%
• B. 38%
• C. 40%
• D. 50%

Answer: (C)

Conduit fill is the main idea here. The NEC limits how much of a conduit’s inner cross-sectional area can be occupied by conductors so there’s room for heat dissipation and easy pulling of wires. For a raceway with four current-carrying conductors, the total cross-sectional area of the conductors (excluding any lead covering) must not exceed 40% of the conduit’s interior cross-sectional area. That makes 40% the correct limit. The other percentages would either impose more restriction than required or exceed the allowed fill (50% would go over the 40% cap).