Four-aught is the last AWG label in this chart. The following rows switch to kcmil, a thousand-circular-mil designation, rather than another aught size. Staying with four-aught only because it is the last gauge can miss a longer run or a terminal-limited load that a later row would still describe. Compare the cells, then put current and distance into the calculator.
Aluminum four-aught remains fully listed. It is not interchangeable with copper four-aught just because the label matches. Bare diameter is the stranded conductor, not the insulated cable and not conduit fill. Parallel conductors are not proposed here; a load that exceeds one conductor needs an engineered layout.
The example current of 200 A does not equal any copper temperature cell for 4/0 AWG. It is above the 60°C copper cell of 195 A, so a 60°C terminal cap does not cover this current before any other correction. The prefilled calculator uses 240 V, 180 ft one way, 75°C insulation, and 75°C terminals. Those are inputs, not a required circuit.
The selected NEC 240.4(D) column in this tool has no special ceiling for 4/0 AWG. A blank is not permission to omit overcurrent protection. Table ampacity, the terminal cap, and voltage drop still apply.
Aluminum 4/0 AWG is listed at 150 A (60°C), 180 A (75°C), and 205 A (90°C), against copper 195 A, 230 A, and 260 A. Stranded resistance at 75°C is 0.1 Ω/kft aluminum and 0.0608 Ω/kft copper. The same label is not the same conductor. Some equipment permits copper only.
This chart’s Table 8 row for 4/0 AWG publishes stranded resistance only (0.0608 Ω/kft copper, 0.1 Ω/kft aluminum). The calculator uses that stranded value.
Table 8 lists 19 strands and 211600 circular mils for 4/0 AWG. The rounded nominal area is 107.2 mm². Bare stranded diameter is 0.528 in, which excludes insulation and is not conduit fill.
| Listing | Copper | Aluminum |
|---|---|---|
| 60°C ampacity (A) | 195 | 150 |
| 75°C ampacity (A) | 230 | 180 |
| 90°C ampacity (A) | 260 | 205 |
| Stranded Ω/kft | 0.0608 | 0.1 |
| Solid Ω/kft | — | — |
| Selected 240.4(D) ceiling (A) | — | — |
| Circular mils | 211600 | |
| Rounded mm² | 107.2 | |
| Strands | 19 | |
| Bare diameter (in) | 0.528 | |
For 4/0 AWG itself, not for whatever size the calculator recommends, Table 8 stranded copper resistance of 0.0608 Ω/kft at 75°C gives 4.38 V (1.82% of 240 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 0.1 Ω/kft give 7.20 V (3.00%). 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 3/0 AWG to 4/0 AWG, the 75°C copper listing goes from 200 A to 230 A. Stranded copper resistance at 75°C goes from 0.0766 Ω/kft to 0.0608 Ω/kft.
The next stored row after 4/0 AWG is 250 kcmil. Its 75°C copper listing is 255 A and its stranded copper resistance is 0.0515 Ω/kft, against 230 A and 0.0608 Ω/kft on 4/0 AWG.
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.
Related guides
Open the wire size calculator · Ampacity chart · Voltage drop calculator · Printable chart