Conduit Fill Calculator

Per NEC Chapter 9, Table 1, when running 3 or more conductors through conduit, the total cross-sectional area of all wires cannot exceed 40% of the conduit's internal area. This limit allows for heat dissipation and makes pulling wires easier without damaging insulation. For 1 wire, the limit is 53%, and for 2 wires, it's 31%.

Yes, equipment grounding conductors (EGC) must be included in conduit fill calculations. All conductors running through the conduit count toward the fill percentage, including ground wires, neutrals, and hot conductors. The only exception is certain cable assemblies where the overall cable diameter is used instead.

When more than 3 current-carrying conductors are in a raceway, you must derate the ampacity per NEC 310.15(C)(1). For 4-6 conductors, derate to 80%. For 7-9 conductors, derate to 70%. For 10-20 conductors, derate to 50%. This is separate from conduit fill calculations and relates to heat buildup affecting wire capacity. Neutral conductors that carry only unbalanced current typically don't count for derating.

EMT (Electrical Metallic Tubing) is thin-walled steel tubing, easiest to work with but not suitable for direct burial. PVC Schedule 40 is plastic conduit for underground and corrosive environments. PVC Schedule 80 has thicker walls for exposed locations. RMC (Rigid Metal Conduit) is the heaviest, most protective option, required in hazardous locations. IMC (Intermediate Metal Conduit) is between EMT and RMC in wall thickness.

Yes, you can mix different wire sizes in the same conduit. Simply add up the cross-sectional area of each wire to calculate total fill. This is common when running circuits with different requirements through the same raceway, such as a 20A circuit alongside a 15A circuit, or when running power and control wiring together.