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Fill Limits — NEC Chapter 9 Table 1

Conductors and/or cablesMaximum fill, % of cross section

Percent of the conduit or tubing cross section, NEC 2017 Chapter 9 Table 1 [1]; nipples: see Note 4 below. Values on this page are from NEC 2017; the site’s calculators each cite the NEC edition their own data came from. To size a raceway for a mix of conductors, use the Conduit Fill calculator.

Notes to the Chapter 9 Tables, in Short

NoteTopicRule (paraphrased)
2Where Table 1 appliesComplete conduit or tubing systems only, not short sleeves protecting exposed wiring from damage.
3Grounding conductorsEquipment grounding or bonding conductors count in the fill, at their actual size, insulated or bare.
4Nipples ≤ 600 mm (24 in.)Between boxes, cabinets and similar enclosures: fill up to 60 % (the Table 4 60 % column).
5Cables not in Chapter 9Multiconductor and optical fiber cables: use their actual dimensions.
6Mixed sizesConductor areas from Table 5 or 5A (or actual), raceway areas from Table 4.
7Counting same-size conductorsRound the maximum number up to the next whole number when its decimal is 0.8 or more. Sizing for one conductor: a result of 0.8 or more permits that one conductor.
8Bare conductorsWhere bare conductors are allowed, the Table 8 dimensions may be used.
9Cables and cordsA multiconductor cable, optical fiber cable or flexible cord counts as one conductor; an elliptical one as a circle of its major diameter. Single conductors grouped without an overall covering are not a cable: count each one.
10Table 5 valuesWorst case, for round concentric-lay stranding (compact stranding is in Table 5A); known actual dimensions may be used instead.
Table 1, Inf. Note 2JammingPulling three conductors or cables: jamming can occur when raceway inside diameter ÷ conductor outside diameter is 2.8 to 3.2.

Paraphrased from NEC 2017 Chapter 9, Notes to Tables and Table 1 Informational Note No. 2 [1]; read the code text before applying.

Conduit & Tubing Dimensions — NEC Chapter 9 Table 4

Trade sizeMetric designatorNominal IDTotal area 100 %60 %1 wire 53 %2 wires 31 %Over 2 wires 40 %
in.in²in²in²in²in²

Insulated Conductor Dimensions — NEC Chapter 9 Table 5

SizeApproximate areaApproximate diameterTable row lists
mm²in²mmin.

Types marked “no outer covering” are RHH, RHW and RHW-2 without their outer covering, which Table 5 lists separately.

Compact Copper & Aluminum Building Wire — NEC Chapter 9 Table 5A

SizeBare conductor diameterApproximate diameterApproximate area
mmin.mmin.mm²in²

Nominal dimensions, which the table takes from industry sources. Type THHN has no 8 AWG row.