Ampacity Chart
Ampacity is the most current a wire can carry continuously without exceeding its temperature rating. This chart lists the NEC Table 310.16 ampacities for copper and aluminum wire from 14 AWG to 1000 kcmil, with the correction factors for hot locations and bundled wires. Use the calculator to find the smallest wire for a load.
Wire size from amps
Minimum wire size
8 AWG copper
Usable ampacity
50 A
Small-wire breaker cap
None for this size
Table 310.16 gives 8 AWG copper 50 A in the 75 °C column. × 1 for ambient temperature × 1 for 3 current-carrying wires = 50 A. The 75 °C terminals cap it at 50 A, so the usable ampacity is 50 A.
A starting point only. Continuous loads, voltage drop, dwelling service rules, and local amendments can change the answer; have a licensed electrician confirm.
Wire ampacity chart (NEC 310.16)
Amps for not more than three current-carrying conductors in raceway, cable, or earth at 30 °C (86 °F). 60 °C covers types TW and UF (and NM-B cable); 75 °C covers THW, THWN, XHHW, and USE; 90 °C covers THHN, THWN-2, XHHW-2, and USE-2.
| Size | Copper 60 / 75 / 90 °C | Aluminum 60 / 75 / 90 °C |
|---|---|---|
| 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 |
| 750 kcmil | 400 / 475 / 535 | 320 / 385 / 435 |
| 1000 kcmil | 455 / 545 / 615 | 375 / 445 / 500 |
Aluminum is not listed for 14 AWG. Diameters, areas, and resistance for each gauge are on the wire gauge chart.
Breaker limits for small wire
NEC 240.4(D) caps the overcurrent protection on small conductors below their table ampacity, unless another section of the code specifically allows more (motor circuits, for example).
| Wire | Max breaker |
|---|---|
| 14 AWG copper | 15 A |
| 12 AWG copper | 20 A |
| 10 AWG copper | 30 A |
| 12 AWG aluminum | 15 A |
| 10 AWG aluminum | 25 A |
Ambient temperature correction
In hot places such as attics, multiply the table ampacity by the factor for the wire's insulation rating (NEC Table 310.15(B)(1)(1)).
| Ambient | 60 °C wire | 75 °C wire | 90 °C wire |
|---|---|---|---|
| 70–77 °F (21–25 °C) | 1.08 | 1.05 | 1.04 |
| 78–86 °F (26–30 °C) | 1.00 | 1.00 | 1.00 |
| 87–95 °F (31–35 °C) | 0.91 | 0.94 | 0.96 |
| 96–104 °F (36–40 °C) | 0.82 | 0.88 | 0.91 |
| 105–113 °F (41–45 °C) | 0.71 | 0.82 | 0.87 |
| 114–122 °F (46–50 °C) | 0.58 | 0.75 | 0.82 |
| 123–131 °F (51–55 °C) | 0.41 | 0.67 | 0.76 |
| 132–140 °F (56–60 °C) | — | 0.58 | 0.71 |
Derating for more than three wires
When more than three current-carrying conductors share a raceway or cable, multiply each one's ampacity by this factor (NEC Table 310.15(C)(1)).
| Current-carrying conductors | Percent of table value |
|---|---|
| 1–3 | 100% |
| 4–6 | 80% |
| 7–9 | 70% |
| 10–20 | 50% |
| 21–30 | 45% |
| 31–40 | 40% |
| 41 or more | 35% |
Example: 10 AWG THHN (90 °C, 40 A) with six current-carrying wires in a 95 °F space: 40 × 0.96 × 0.80 = 30.7 A, which is under the 35 A limit of 75 °C terminals, so 30.7 A is usable.
Ampacity Chart FAQ
What size wire do I need for 50 amps?
Using the 75 °C column, 8 AWG copper (50 A) or 6 AWG aluminum (50 A). If the terminals or cable are limited to 60 °C, as with NM-B, you need 6 AWG copper (55 A).
What size wire do I need for 100 amps?
Using the 75 °C column, 3 AWG copper (100 A) or 1 AWG aluminum (100 A). Services and main feeders for homes have a separate sizing rule in the NEC, so the right size for a 100 A house service can differ; ask an electrician.
What is the ampacity of 12 gauge wire?
12 AWG copper is 20 A at 60 °C, 25 A at 75 °C, and 30 A at 90 °C in Table 310.16, but NEC 240.4(D) limits the breaker on it to 20 A. 12 AWG aluminum is 15/20/25 A, with a 15 A breaker limit.
Why is aluminum wire rated for fewer amps than copper?
Aluminum conducts about 61% as well as copper, so the same size wire heats up more at the same current. That is why aluminum is usually one or two sizes larger than copper for the same load.
Which temperature column should I use?
Start with the column for the wire's insulation, apply any derating, then make sure the result does not exceed the column for the lowest-rated terminal in the circuit (NEC 110.14(C)). Most breakers and lugs are rated 60 or 75 °C, so a 90 °C wire like THHN is usually limited to its 75 °C or 60 °C value; the 90 °C value is mainly a starting point for derating.
Sources
Ampacities are NFPA 70 (National Electrical Code) Table 310.16, as reproduced in NFPA's Code-Making Panel 6 report, checked against Cerrowire's ampacity chart and earlier printings of the table. Correction and adjustment factors are NEC Tables 310.15(B)(1)(1) and 310.15(C)(1), checked against an electrician exam study guide. Breaker limits are NEC 240.4(D).
Table values assume no more than three current-carrying conductors in a 30 °C (86 °F) ambient. Your local code edition and amendments apply; have a licensed electrician confirm wire sizes for any real installation.