The National Electrical Code establishes maximum conduit fill based on conductor count: Diagram illustrating conduit fill percentages for 1, 2, and 3+ conductors based on NEC guidelines. 💡 Key Insight: The 40% fill rule for three or more conductors is most commonly used in. This guide provides the charts, calculations, and practical examples you need to size conduits correctly every time. Source: NEC 2023, Chapter 9, Tables 1, 4 & 5 · Reviewed: 2026-03-28 · Fill limits: 53% (1 wire), 31% (2 wires), 40% (3+ wires). Works with EMT, PVC, and RMC conduits with accurate wire area calculations for safe installations.