Metallic Wireway Selection (Reference NFPA 70, National Electrical Code)

UsesUses Permitted for Metallic Wireways:

1. For exposed work.2. In concealed spaces as permitted in NEC section 376.10.3. In hazardous (classified) locations as permitted by NEC® articles 501, 502, and 504.4. As extension through walls if the length passing through a wal is unbroken and access to conductors can be mained from both sides.

Uses NOT Permitted for Metallic Wireways:1. Where subject to severe physical damage.2. Where subject to severe corrosive environments.

Size of ConductorsTable 1 shows maximum conductor size based on bending space, (UL Standard 870, Table 7.1)

Table 1

Wireway size Max. Cable Size4"x4" 16 4/O6"x6" 36 5008"x8" 64 900

Number and Ampacity of Conductors1. Sum of the cross-sectional area of all conductors contained in the wireway at any cross section shall not exceed 20% of the

interior cross-sectional area of the wireway. See Table 2 for allowable conductor cross-sectional areas.2. Wireways containing (30) current conductors or less are not subject to adjustment factors.3. Wireway exceeding (30) current carrying conductors shall be subject to adjustment factors as defined in NEC Article 376.22(8).

Table 2

Wireway size4"x4" 3.26"x6" 7.28"x8" 12.8

Splices and TapsSplices and taps are permitted within a wireway, provided they are accessible. The conductors, includingsplices and taps, shall not fill the wireway to more than 75 percent of its area at the point of a splice or tap.

Cross Section (in2)

Allowable Cable Area (in2)

SupportsHorizontal supports shall be supported at each end and at intervals not exceeding 10 feet. Vertical supports shall be supported at intervals not exceeding 15 feet and shall not have more than (1) joint between support.

Metallic Wireway Selection (Reference NFPA 70, National Electrical Code)

4. As extension through walls if the length passing through a wal is unbroken and access to conductors can be mained from both sides.

1. Sum of the cross-sectional area of all conductors contained in the wireway at any cross section shall not exceed 20% of the interior cross-sectional area of the wireway. See Table 2 for allowable conductor cross-sectional areas.

3. Wireway exceeding (30) current carrying conductors shall be subject to adjustment factors as defined in NEC Article 376.22(8).

Splices and taps are permitted within a wireway, provided they are accessible. The conductors, includingsplices and taps, shall not fill the wireway to more than 75 percent of its area at the point of a splice or tap.

Vertical supports shall be supported at intervals not exceeding 15 feet and shall not have more than (1) joint between support.

Wireway Sizing Calculator DirectionsInputs

Conductor Diameter, A (inches) 1) Wireway systems allow multiple conductors sizes within a wireway. The size of wireway required Number of Conductors, A (inches) is a function of the cross-sectional area of the cables but is also limited by the cable bending requirements

of the largest conductor.Conductor Diameter, B (inches) 2) This tool calculates the recommended wireway size and allows up to 3 different cable diameter inputs.Number of Conductors, B (inches) 3) Enter the cable diameter and number of cables in the yellow cells. If only one cable size is being used

then leve inputs B & C blankConductor diameter, C (inches) 4) Also input the largest conductor type in this section.Number of Conductors, C (inches)

Largest Conductor Type 10

Calculations

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Wireway Size by Cable Fill 4"x4"Wireway Size by Max Conductor Type 4"x4"

RecommendationRecommended Wireway Size 4"x4"

at any cross section, cable derating may be required (see NEC® 362-5)

Cable Cross Sectional Area (in2)

Wireway Cross Sectional Requirements (in2)

Note: if more than 30 current-carrying conductors are present

Wireway systems allow multiple conductors sizes within a wireway. The size of wireway required is a function of the cross-sectional area of the cables but is also limited by the cable bending requirements of the largest conductor.

This tool calculates the recommended wireway size and allows up to 3 different cable diameter inputs.Enter the cable diameter and number of cables in the yellow cells. If only one cable size is being used

then leve inputs B & C blankAlso input the largest conductor type in this section.

<- The recommended wireway size is displayed here.