# Unit 05: Raceway, Conductors, and Box Calculations

### NEC Chaper 9, Annex C, Article 300, 314, 376

#### NEC Code Book

• Annex C
• raceway interior cross-sectional area maximum fill-limit percentages by conductors of the same size
• NEC Ch.09, Table 1
• raceway interior cross-sectional area maximum fill-limit percentages by conductors
• raceways 2′ or less can be filled to 60%
• When raceway ID is between 2.8 to 3.2 x the conductor diameter, jamming can occur
• NEC Ch.09, Table 4
• Raceways cross-sectional area and fill percent area
• Various raceway types with columns representing allowable percentage fills
• Use caution when selection raceway
• divided into numerous tables for each raceway type
• must choose the correct table section for the raceway type performing calculations on
• NEC Ch.09, Table 5
• Conductor cross-sectional area, round, concentric-lay-stranded, giving worst-case scenario
• Note: concentric is multiple circles sharing the same center
• NEC Ch.09, Table 5A
• Conductor cross-sectional area, round, compact-stranded, giving worst-case scenario
• NEC Ch.09, Table 8
• Conductor cross-sectional area, round, concentric-lay-stranded, uninsulated, giving worst-case scenario
• Circular mils table
• number of strands per conductor
• 4th column – ‘Stranding’, ‘Quantity’
• ‘1’ denotes solid conductor
• DC resistance @ 75°
• NEC Ch.09, Table Notes
• Note (1) Use Annex C with same size conductors
• Note (2) Table 1 doesn’t apply to raceways used for conductor protection
• Note (3) When calculating raceway fill, use equipment grounding and bonding conductors area too
• Note (4) Raceways 2′ or less can be filled to 60%
• Note (5) With Chapter 9 not-included conductors (multi-conductor & optical fiber), use actual dimensions
• Note (6) Tables 4, 5, 5A summaries
• Note (7) When using Annex C, calculating # of same-size conductors to fill conduit/tubing, round up to whole # when decimal  ≥ 0.8
• Note (8) Table 8, bare conductors
• Note (9) With elliptical cables (multi-conductor & optical fiber), use larger cross-section
• If only cable diameter is given, determine the conductor Sq in. area using this forumla
• Conductor Area = Area = 3.14 x (Dia. x ½)2
• Note (10) Tables 5, 5A summaries
• Table 310.104(A)
• Conductor Applications and Insulation
• differences in conductor insulation thickness
• Table 314.16(A)
• outlet boxes conductor limits

### Conductors

• Conductor Area
• Area = 3.14 x (Dia. x ½)2
• Raceway fill Limitation Ratio
• Ratio = Raceway Diameter / Conductor Diameter

### Raceways

• Distance between raceways enclosing the same conductor must not be closer than 6 times the trade size of the largest raceway measured from nearest edges
• Conductors 8 AWG & larger must be stranded when installed in a raceway
• 310.106(C)
• #### Raceway Trade Size

• use Ch.9-Table 4
• #### Metal Wireways

• Article 376
• Limits conductor cross-sectional area , number of conductors, wire-bend radius,
• #### Raceway Sizing

• 300.17
• Raceway Sizing StepsNEC-2017 ReferenceNotesShorthand
Determine each conductors cross-sectional areaCh9-Table 5Insulated conductorsconductor x-sec area
Ch9-Table 8Bare conductorsconductor total x-sec area
Determine total cross-sectional area for all conductors
Size raceway according to percent fillCh9-Table 1raceway % fill
Ch9-Table 4see notes above
• #### Raceways with multiple Rows

1. Calculate each row individually as shown above
2. Use row with largest distance
• #### Raceway fill Limitation Ratio

• Ratio = Raceway Diameter / Conductor Diameter
• Ratio between 2.8 to 3.2 can cause jamming

### Electrical Outlet Box Fill

• 314.16
• Calculations:
1. Determine conductor number & sizes within the box
2. Determine conductor volume equivalents from Table 314.16(B)
3. Size box using Table 314.16(A)
• Conductors same-size = add together & size box using Table 314.16(A)-AWG size columns
• Conductors different sizes = Finds area of each conductor using Table 314.16(B), add them up, size box using Table 314.16(A)-cu” column
• Draw out picture to problem solve
• Volume of box calculated by 314.16(A) can never be less than the volume required by calculations based on 314.16(B)

#### Go over pages 209-214, this is complicated

• Insulation type is not a sizing factor with Box Fill calculations
• Table 314.16(A)
• Determine outlet box size required for given number of same-sized conductors and number of conductors permitted within
• Table does not reflect need for allowance for switches, respectacles, etc.
• Box Volume Barriers
• if unmarked:
• ½ in3 if metallic
• 1 inif non-metallic
• 314.16(B)(1) through (5)
• determines total volume of conductors. devices, & fittings
1. Conductor Volume
• Count as a single conductor every conductor running through a box and each conductor terminating in a box (314.16(B)
• Count loops 12″ or longer as 2 conductors (300.14)
• Conductors looping through box 12″ or less are not counted
2. Cable Clamp Volume
• based on largest entering conductor, all internal cable clamps count as 1 conductor
• Clamping mechanisms outside the box count for 0
3. Support Fitting Volume
• based on largest entering conductor, each luminaire stud or hickey is counted as 1 single conductor volume
4. Device Yoke Volume
• based on largest entering conductor
• each single-gang device yoke is counted as 2 conductor volumes
• each multigang device yoke is counted as 2 conductor volumes
5. Equipment Grounding Conductor Volume
• Count all entering as 1 using size from largest entering box
• Use all attached to receptacles as 1
• 314.28
• Conductors 4 AWG and larger
• Box Sizing Formulas
• Remaining Space = Total space less the area required for existing conductors
• Conductors added = Remaining space / Added Conductors Volume

### Junction Boxes, Pull Boxes, and Conduit Bodies

• Junction box & pull box calculations only calculated when conductor sizes are 4 AWG & larger
• 314.28
• Conductors 4 AWG and larger requiring insulation
• Minimum sizes
• Straight Pulls
• When  a conductor enters and than exits on the opposite wall
• Minimum box dimension must not be less than 8 times the trade size of the largest raceway
• Straight Pull calculation required when conductor enters one side and exits on the opposite wall
• Angle Pulls
• When  a conductor enters and than exits 90° from the entrance wall
• Minimum box dimension must not be less than 6 times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall
• U Pulls
• When  a conductor enters and exits on the same wall
• Minimum box dimension must not be less than 6 times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall
• Splices
• When  a conductor is spliced
• Distance from where the raceways enter to the opposite wall must not be less than 6 times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall
• To size boxes, calculate:
1. Minimum box size, and
2. Distance between raceways, and
3. possibly multiple row calculations
• MH-pg 215-216
• Box sizing tips
• Draw out problem
• Calculate horizontal
• Left-to-right, straight
• Right-to-left, straight
• Left-to-right angle &/or U-pull
• Right-to-left angle &/or U-pull
• Calculate Vertical
• Top-to-Bottom, straight
• Bottom-to-Top, straight
• Top-to-Bottom angle &/or U-pull
• Bottom-to-Top angle &/or U-pull
• Calculate raceway distances enclosing same conductor
• Problem examples in MH-pg 217