Methodology & Sources

27 constants and where they come from

• AWG/kcmil conductor circular milsconfidence: physical
  Ref: Physical conversion: 1 mil = 0.001 in; circular mils = diameter (mil)^2
  verified: pending
• AWG/kcmil to mm² conversion (1 circular mil = 0.0005067074791 mm²)confidence: physical
  Ref: Physical conversion: 1 circular mil = pi/4 x (0.0254 mm)^2, since 1 mil = 0.001 in
  verified: pending
• Metric nominal cross-sectional area series (IEC 60228, 0.5 mm² to 1000 mm²)confidence: physical
  Ref: IEC 60228 nominal cross-sectional areas
  verified: pending
• IEC metric ampacity, copper with PVC insulation at 70°C (air, 30°C reference)confidence: code-table
  Ref: IEC 60364-5-52:2009 with AC1:2011, Tables B.52.2 (2 loaded conductors) and B.52.4 (3 loaded conductors)
  verified: pending
• IEC metric ampacity, copper with XLPE/EPR insulation at 90°C (air, 30°C reference)confidence: code-table
  Ref: IEC 60364-5-52:2009, Tables B.52.3 (2 loaded conductors) and B.52.5 (3 loaded conductors)
  verified: pending
• Voltage-drop resistance constant K (copper 12.9 / aluminum 21.2 ohm-cmil/ft)confidence: engineering
  Ref: Derived from NEC Chapter 9, Table 8 resistance values; common engineering approximation
  verified: pending
• Conductor ampacity base table (60/75/90°C)confidence: code-table
  Ref: NEC 310.16
  verified: pending
• Ambient temperature correction factor, 30°C baseconfidence: code-table
  Ref: NEC Table 310.15(B)(1)(1)
  verified: pending
• Adjustment factor for conductor count in a racewayconfidence: code-table
  Ref: NEC 310.15(C)(1)
  verified: pending
• Termination temperature limit (explicit 60°C or 75°C column)confidence: code-table
  Ref: NEC 110.14(C)
  verified: pending
• Conduit fill percentage (1 conductor 53% / 2 conductors 31% / 3 or more 40%)confidence: code-table
  Ref: NEC Chapter 9, Table 1 and Note 7
  verified: pending
• Conduit internal diameter and total internal areaconfidence: code-table
  Ref: NEC Chapter 9, Table 4
  verified: pending
• Conductor cross-sectional area (THHN/THWN and similar)confidence: code-table
  Ref: NEC Chapter 9, Table 5
  verified: pending
• Box volume allowances and minimum box volume requirementsconfidence: code-table
  Ref: NEC 314.16
  verified: pending
• Standard overcurrent protective device ratingsconfidence: code-table
  Ref: NEC 240.6(A)
  verified: pending
• Small-conductor overcurrent protection limits (14/12/10 AWG)confidence: code-table
  Ref: NEC 240.4(D)
  verified: pending
• Continuous loads: 125% for the overcurrent device and the termination column, 100% for corrected ampacityconfidence: code-table
  Ref: NEC 210.20(A)
  verified: pending
• Branch-circuit voltage drop recommendation of 3% or less, and 5% combined (informational note)confidence: code-table
  Ref: NEC 210.19(A)(1) Informational Note
  verified: pending
• Recessed light count and spacing (target fc x area / (lumens x CU x LLF))confidence: engineering
  Ref: Lighting design arithmetic; the rule-of-thumb spacing is half the ceiling height and is not an NEC requirement
  verified: pending
• Conditional next-higher standard overcurrent device exceptionconfidence: code-table
  Ref: NEC 240.4(B)
  verified: pending
• IEC metric ampacity, aluminium, verified from 16 mm²confidence: code-table
  Ref: IEC 60364-5-52:2009, Tables B.52.2 to B.52.5
  verified: pending
• IEC air ambient-temperature correction factorsconfidence: code-table
  Ref: IEC 60364-5-52:2009, Table B.52.14
  verified: pending
• IEC grouping correction factors for circuits in airconfidence: code-table
  Ref: IEC 60364-5-52:2009, Table B.52.17
  verified: pending
• IEC soil-temperature correction factors for buried cablesconfidence: code-table
  Ref: IEC 60364-5-52:2009, Table B.52.15
  verified: pending
• IEC grouping factors for buried multi-core cables, method D2confidence: code-table
  Ref: IEC 60364-5-52:2009, Table B.52.18
  verified: pending
• IEC grouping factors for buried ducts, method D1confidence: code-table
  Ref: IEC 60364-5-52:2009, Table B.52.19
  verified: pending
• Feeder voltage drop recommendation of 3% or less, and 5% combined (informational note)confidence: code-table
  Ref: NEC 215.2(A)(1) Informational Note
  verified: pending