Fourteen AWG is the smallest copper size this calculator offers for a general power circuit. A single breaker number cannot describe all three copper temperature cells and the separate small-conductor overcurrent ceiling. Those columns do different jobs. A hotter insulation listing does not, by itself, raise the ordinary device above that ceiling, and this page does not evaluate equipment exceptions.
Aluminum at this label has no ampacity cells at all. The blanks are empty listings, not a zero-amp conductor you can “round up.” Stranded aluminum resistance can still appear in the resistance table; a resistance without an ampacity listing is not an allowable aluminum size here. On a long low-voltage branch, voltage drop often becomes the reason a larger copper size shows up in the calculator even when the ampacity cell looked sufficient.
The example current of 15 A equals the copper listing at 60°C. The prefilled calculator uses 120 V, 50 ft one way, 60°C insulation, and 60°C terminals. Those are inputs, not a required circuit.
The selected NEC 240.4(D) ceilings in this tool are copper 15 A. Those are ordinary overcurrent-device limits, not extra ampacity, and they are not a complete breaker-selection procedure. Equipment exceptions are not checked.
Table 310.16 has no aluminum ampacity listing for 14 AWG. Stranded aluminum resistance is still published as 5.17 Ω/kft. A resistance without an ampacity listing is not an allowable aluminum conductor in this chart.
Table 8 also lists solid copper 3.07 Ω/kft and solid aluminum 5.06 Ω/kft beside stranded copper 3.14 Ω/kft and stranded aluminum 5.17 Ω/kft. The calculator’s sizing path uses the stranded column.
Table 8 lists 7 strands and 4110 circular mils for 14 AWG. The rounded nominal area is 2.08 mm². Bare stranded diameter is 0.073 in, which excludes insulation and is not conduit fill.
| Listing | Copper | Aluminum |
|---|---|---|
| 60°C ampacity (A) | 15 | — |
| 75°C ampacity (A) | 20 | — |
| 90°C ampacity (A) | 25 | — |
| Stranded Ω/kft | 3.14 | 5.17 |
| Solid Ω/kft | 3.07 | 5.06 |
| Selected 240.4(D) ceiling (A) | 15 | — |
| Circular mils | 4110 | |
| Rounded mm² | 2.08 | |
| Strands | 7 | |
| Bare diameter (in) | 0.073 | |
For 14 AWG itself, not for whatever size the calculator recommends, Table 8 stranded copper resistance of 3.14 Ω/kft at 75°C gives 4.71 V (3.92% of 120 V) using 2 × I × R × L / 1,000. Reactance is omitted. Displayed volts are rounded to two decimals. The same inputs with stranded aluminum resistance 5.17 Ω/kft give 7.75 V (6.46%). If that percentage is outside the prefilled drop limit, the calculator will name a different size. That is the voltage-drop check, not a second ampacity table.
From 14 AWG to 12 AWG, the 75°C copper listing goes from 20 A to 25 A. Stranded copper resistance at 75°C goes from 3.14 Ω/kft to 1.98 Ω/kft.
Planning estimate only. Consult local code and a qualified electrician before buying wire or energizing a circuit. Presets are hypothetical loads; this tool does not design motor, PV, battery, appliance, or EV installations.
Sources for these cells: existing Table 310.16 numerical cells in NFPA’s public development record, pp. 142–143 (proposed changes are not treated as adopted code) and NFPA 70 (2017), Chapter 9 Table 8, printed p. 689, in a third-party-hosted copy. The same publication supplies 110.14 (terminals and aluminum), 210.19/215.2 (continuous loads), 240.4(D) (small conductors), 250.24/250.32 (grounding), and 625.41/625.42 (EV loads). Schneider Electric’s voltage-drop formulas support the arithmetic; Table 8 AC results here omit reactance and assume unity power factor. Resistance and geometry are construction- and temperature-specific. Adopted editions and local amendments can differ.
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