WIRE·FILL·CHARTNEC 2023 · CH. 9
DOC · CITATION INDEX

NEC
REFERENCES

Every cell in the WireFillChart wire fill chart and every result from the conduit fill calculator traces back to one of the articles below. Buy the full NEC from NFPA — we publish derived calculations, not redistributed code text.

FIG. 01

CONDUIT FILL BASICS

  • 01CH.9 TABLE 1

    Percent of Cross-Section of Conduit and Tubing for Conductors

    Sets the 53 / 31 / 40 percent fill rule by conductor count, plus the 60% nipple allowance.

  • 02CH.9 TABLE 4

    Dimensions and Percent Area of Conduit and Tubing

    Interior cross-sectional area for every conduit type at every trade size — Article 342 (IMC), 344 (RMC), 348 (FMC), 352 (PVC), 356 (LFNC), 358 (EMT), 362 (ENT).

  • 03CH.9 TABLE 5

    Dimensions of Insulated Conductors and Fixture Wires

    Cross-sectional area of every common insulation × every gauge — THHN, THWN, THWN-2, XHHW, XHHW-2, RHH, RHW, RHW-2, TW, TFE.

FIG. 02

ADJUSTMENTS OUTSIDE FILL

  • 01310.15(B)(1)

    Ambient Temperature Correction

    Correction factors when raceway ambient differs from 30 °C — independent of fill %.

  • 02310.15(C)(1)

    More Than Three Current-Carrying Conductors

    Ampacity adjustment factor: 80% for 4–6 CCCs, 70% for 7–9, 50% for 10–20, 45% for 21–30, 40% for 31–40, 35% for 41+. Applies independently of conduit fill %.

  • 03310.16

    Ampacity Table for 0–2000 V Insulated Conductors

    Baseline ampacity by gauge and insulation temperature rating.

  • 04ANNEX C

    Conduit and Tubing Fill Tables

    Precomputed max-conductor tables that occasionally round differently than the strict Table 4 × Table 5 calculation.

FIG. 03

RACEWAY ARTICLES

  • 01ART. 358

    Electrical Metallic Tubing (EMT)

    Installation rules, supports, bends, and permitted uses.

  • 02ART. 344

    Rigid Metal Conduit (RMC)

    Hazardous-location applications, threaded fittings.

  • 03ART. 342

    Intermediate Metal Conduit (IMC)

    Lighter-weight rigid alternative to RMC.

  • 04ART. 352

    Rigid PVC Conduit

    Schedule 40 and Schedule 80, including expansion fittings (352.44).

  • 05ART. 348

    Flexible Metal Conduit (FMC)

    Limits on use as equipment ground (over 6 ft requires separate EGC).

  • 06ART. 356

    Liquidtight Flexible Nonmetallic Conduit (LFNC)

    Direct sunlight, oil, wet-location rating.

  • 07ART. 362

    Electrical Nonmetallic Tubing (ENT)

    Dry/concealed indoor use, height-of-building limits.