Unit 05: Raceway, Conductors, and Box Calculations
NEC Chaper 9, Annex C, Article 300, 314, 376
NEC Code Book
 Annex C
 raceway interior crosssectional area maximum filllimit percentages by conductors of the same size
 NEC Ch.09, Table 1
 raceway interior crosssectional area maximum filllimit 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 crosssectional 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 crosssectional area, round, concentriclaystranded, giving worstcase scenario
 Note: concentric is multiple circles sharing the same center
 Conductor crosssectional area, round, concentriclaystranded, giving worstcase scenario
 NEC Ch.09, Table 5A
 Conductor crosssectional area, round, compactstranded, giving worstcase scenario
 NEC Ch.09, Table 8
 Conductor crosssectional area, round, concentriclaystranded, uninsulated, giving worstcase 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 notincluded conductors (multiconductor & optical fiber), use actual dimensions
 Note (6) Tables 4, 5, 5A summaries
 Note (7) When using Annex C, calculating # of samesize conductors to fill conduit/tubing, round up to whole # when decimal ≥ 0.8
 Note (8) Table 8, bare conductors
 Note (9) With elliptical cables (multiconductor & optical fiber), use larger crosssection
 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}
 If only cable diameter is given, determine the conductor Sq in. area using this forumla
 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.9Table 4

Metal Wireways
 Article 376
 Limits conductor crosssectional area , number of conductors, wirebend radius,

Raceway Sizing
 300.17

Raceway Sizing Steps NEC2017 Reference Notes Shorthand Determine each conductors crosssectional area Ch9Table 5 Insulated conductors conductor xsec area Ch9Table 8 Bare conductors conductor total xsec area Determine total crosssectional area for all conductors Size raceway according to percent fill Ch9Table 1 raceway % fill Ch9Table 4 see notes above

Raceways with multiple Rows
 Calculate each row individually as shown above
 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:
 Determine conductor number & sizes within the box
 Determine conductor volume equivalents from Table 314.16(B)
 Size box using Table 314.16(A)
 Conductors samesize = 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 209214, 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 samesized conductors and number of conductors permitted within
 Table does not reflect need for allowance for switches, respectacles, etc.
 Box Volume Barriers
 if unmarked:
 ½ in^{3} if metallic
 1 in^{3 }if nonmetallic
 if unmarked:
 314.16(B)(1) through (5)
 determines total volume of conductors. devices, & fittings
 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
 Cable Clamp Volume
 based on largest entering conductor, all internal cable clamps count as 1 conductor
 Clamping mechanisms outside the box count for 0
 Support Fitting Volume
 based on largest entering conductor, each luminaire stud or hickey is counted as 1 single conductor volume
 Device Yoke Volume
 based on largest entering conductor
 each singlegang device yoke is counted as 2 conductor volumes
 each multigang device yoke is counted as 2 conductor volumes
 based on largest entering conductor
 Equipment Grounding Conductor Volume
 Count all entering as 1 using size from largest entering box
 Use all attached to receptacles as 1
 Conductor Volume
 determines total volume of conductors. devices, & fittings
 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
 Straight Pulls
 To size boxes, calculate:
 Minimum box size, and
 Distance between raceways, and
 possibly multiple row calculations
 MHpg 215216
 Box sizing tips
 Draw out problem
 Calculate horizontal
 Lefttoright, straight
 Righttoleft, straight
 Lefttoright angle &/or Upull
 Righttoleft angle &/or Upull
 Calculate Vertical
 ToptoBottom, straight
 BottomtoTop, straight
 ToptoBottom angle &/or Upull
 BottomtoTop angle &/or Upull
 Calculate raceway distances enclosing same conductor
 Problem examples in MHpg 217