NEC ampacity chart: Table 310.16
Allowable ampacities of insulated copper and aluminum conductors, 14 AWG to 2000 kcmil, at 30 °C (86 °F) ambient with not more than three current-carrying conductors in the raceway or cable. Cells marked * are limited further by 240.4(D). Below the table: the ambient temperature correction factors and the adjustment for more conductors, the two numbers every derating multiplies by. To skip the arithmetic, the wire size calculator applies all of them.
Table 310.16: allowable ampacities (A)
| Size | Cu 60 °C | Cu 75 °C | Cu 90 °C | Al 60 °C | Al 75 °C | Al 90 °C |
|---|---|---|---|---|---|---|
| 18 AWG | — | — | 14 | — | — | — |
| 16 AWG | — | — | 18 | — | — | — |
| 14 AWG | 15* | 20* | 25* | — | — | — |
| 12 AWG | 20* | 25* | 30* | 15* | 20* | 25* |
| 10 AWG | 30* | 35* | 40* | 25* | 30* | 35* |
| 8 AWG | 40 | 50 | 55 | 35 | 40 | 45 |
| 6 AWG | 55 | 65 | 75 | 40 | 50 | 55 |
| 4 AWG | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 AWG | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 AWG | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 AWG | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 AWG | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 AWG | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 AWG | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 AWG | 195 | 230 | 260 | 150 | 180 | 205 |
| 250 kcmil | 215 | 255 | 290 | 170 | 205 | 230 |
| 300 kcmil | 240 | 285 | 320 | 195 | 230 | 260 |
| 350 kcmil | 260 | 310 | 350 | 210 | 250 | 280 |
| 400 kcmil | 280 | 335 | 380 | 225 | 270 | 305 |
| 500 kcmil | 320 | 380 | 430 | 260 | 310 | 350 |
| 600 kcmil | 350 | 420 | 475 | 285 | 340 | 385 |
| 700 kcmil | 385 | 460 | 520 | 315 | 375 | 425 |
| 750 kcmil | 400 | 475 | 535 | 320 | 385 | 435 |
| 800 kcmil | 410 | 490 | 555 | 330 | 395 | 445 |
| 900 kcmil | 435 | 520 | 585 | 355 | 425 | 480 |
| 1000 kcmil | 455 | 545 | 615 | 375 | 445 | 500 |
| 1250 kcmil | 495 | 590 | 665 | 405 | 485 | 545 |
| 1500 kcmil | 525 | 625 | 705 | 435 | 520 | 585 |
| 1750 kcmil | 545 | 650 | 735 | 455 | 545 | 615 |
| 2000 kcmil | 555 | 665 | 750 | 470 | 560 | 630 |
Ambient temperature correction, Table 310.15(B)(1)(1)
| Ambient °C | Ambient °F | 60 °C | 75 °C | 90 °C |
|---|---|---|---|---|
| 10 or less | 50 or less | 1.29 | 1.20 | 1.15 |
| 11–15 | 51–59 | 1.22 | 1.15 | 1.12 |
| 16–20 | 60–68 | 1.15 | 1.11 | 1.08 |
| 21–25 | 69–77 | 1.08 | 1.05 | 1.04 |
| 26–30 | 78–86 | 1.00 | 1.00 | 1.00 |
| 31–35 | 87–95 | 0.91 | 0.94 | 0.96 |
| 36–40 | 96–104 | 0.82 | 0.88 | 0.91 |
| 41–45 | 105–113 | 0.71 | 0.82 | 0.87 |
| 46–50 | 114–122 | 0.58 | 0.75 | 0.82 |
| 51–55 | 123–131 | 0.41 | 0.67 | 0.76 |
| 56–60 | 132–140 | — | 0.58 | 0.71 |
| 61–65 | 141–149 | — | 0.47 | 0.65 |
| 66–70 | 150–158 | — | 0.33 | 0.58 |
| 71–75 | 159–167 | — | — | 0.50 |
| 76–80 | 168–176 | — | — | 0.41 |
| 81–85 | 177–185 | — | — | 0.29 |
More than three current-carrying conductors, Table 310.15(C)(1)
| Current-carrying conductors | Percent of the table value |
|---|---|
| 1–3 | 100 % |
| 4–6 | 80 % |
| 7–9 | 70 % |
| 10–20 | 50 % |
| 21–30 | 45 % |
| 31–40 | 40 % |
| 41 and above | 35 % |
Reading the chart: one derating, start to finish
Six current-carrying 10 AWG THHN copper conductors in one conduit through a 38 °C attic. Start in the 90 °C column because THHN is a 90 °C insulation: 40 A. Correct for the ambient (36–40 °C at 90 °C): × 0.91. Adjust for four to six conductors: × 0.80. Result: 40 × 0.91 × 0.80 = 29.1 A.
Two ceilings then apply. The termination: on a circuit of 100 A or less the 60 °C column governs unless the breaker and device are marked 75 °C, so the conductor may not be credited with more than 30 A (60 °C) or 35 A (75 °C). And 240.4(D): 10 AWG copper may not be protected above 30 A. So the conductor is good for 29.1 A of load; whether the next standard breaker above that is permitted is a 240.4(B) question for the electrician, not something this page decides. Open this run in the calculator.
Questions people ask
- What is the ampacity of 12 AWG copper wire?
- Table 310.16 lists 20 A at 60 °C, 25 A at 75 °C and 30 A at 90 °C. 240.4(D) still limits the overcurrent protection of 12 AWG copper to 20 A, so the 25 and 30 A figures only matter as the starting point for derating.
- Why is 14 AWG rated 20 A in the 75 °C column but put on a 15 A breaker?
- Because 240.4(D) caps the overcurrent device for small conductors after any correction and adjustment: 15 A for 14 AWG copper, 20 A for 12 AWG, 30 A for 10 AWG; 15 A for 12 AWG aluminum and 25 A for 10 AWG aluminum. The table ampacity and the breaker limit are separate rules.
- Is Table 310.16 the same as Table 310.15(B)(16)?
- Yes. The 2020 NEC renumbered Table 310.15(B)(16) as Table 310.16; the 2023 edition keeps that number. Every cell printed here is identical between the 2017 and the 2023 reproductions this site checked.
- Which temperature column do I use?
- The lowest-rated part of the circuit sets it, and that is usually the termination. 110.14(C) treats terminals on circuits of 100 A or less (or marked for 14 to 1 AWG) as 60 °C unless they are listed and marked 75 °C, and larger ones as 75 °C. The 90 °C column of THHN or XHHW-2 is the starting point for derating, and the derated result may not exceed the termination column.
- What does “not more than three current-carrying conductors” mean?
- The table assumes three or fewer conductors carrying current in the raceway or cable. With four to six the ampacity is multiplied by 0.80, seven to nine by 0.70, ten to twenty by 0.50 (Table 310.15(C)(1)). Equipment grounding conductors never count; a neutral that carries only the unbalanced current of a multiwire circuit does not count either.
- How much less does aluminum carry than copper?
- Roughly two sizes. In the 75 °C column 1 AWG aluminum carries 100 A, the same as 3 AWG copper; 250 kcmil aluminum carries 205 A against 200 A for 3/0 copper.
- Does the ambient correction apply in a normal room?
- The table is based on 30 °C (86 °F). Between 26 and 30 °C the factor is 1.00; above that it falls, for example to 0.91 for a 90 °C conductor at 36 to 40 °C. Below 26 °C the factors exceed 1.00 and can raise the ampacity.