A lot of people size wire off the wrong number. They see “90°C” on a spool of THHN, go to the highest rating on the chart, and build the circuit around that. But the wire usually isn’t what limits you. The terminals are. Each AWG size has three ampacity ratings in NEC Table 310.16, one for 60°C, one for 75°C, and one for 90°C, and which one you can use depends on what your equipment terminals are rated for. That’s the part that decides everything else on the chart. Treat this chart as a sizing reference only: the final conductor size should always be confirmed against the NEC edition adopted in your jurisdiction, the equipment nameplate and listing, and the judgment of a licensed electrician or engineer.
What Is Wire Ampacity?
Ampacity is how much current a wire can carry all day long without getting hotter than its insulation can take. In real projects, a wire that’s too small doesn’t always fail on the spot. It just runs a little too hot, over and over, until the insulation dries out, cracks, and turns into a fire and shock risk. That’s why sizing a conductor starts with ampacity. Pick a gauge that can handle the load that stays on, then check the terminal ratings, derating, and voltage drop before you call the size final. Because that damage builds up slowly, the quality of the insulation matters just as much as the gauge you choose. At ANPU Cable, that’s the part we focus on with our building wire. Rather than relying on the printed rating alone, we back the 90°C rating with checks such as insulation-resistance testing, heat-aging (thermal endurance) evaluation, and batch quality control against the applicable UL/IEC and internal specifications, so a conductor rated for 90°C keeps taking that heat year after year.
How NEC Table 310.16 sets the standard
In North America, conductor sizing usually starts with NFPA 70, the National Electrical Code. NEC Table 310.16 (formerly 310.15(B)(16)) lists the base ampacity values for copper, aluminum, and copper-clad aluminum conductors installed in raceway, cable, or earth. For most residential, commercial, and light-industrial wire calculations, this table is the first reference point before terminal ratings, derating factors, and voltage drop are checked.
The three temperature ratings: 60°C, 75°C, and 90°C
The 60°C, 75°C, and 90°C columns are not interchangeable. Each one is tied to conductor insulation and, more importantly, to the temperature rating of the equipment terminals. In project reviews, one of the most common sizing mistakes we see is treating the 90°C THHN value as the final ampacity while the breaker, lug, or panelboard terminal is only rated 75°C. In that case, the 90°C number may be used for derating calculations, but it does not set the final allowable ampacity.
- 60°C – Used for many smaller residential circuits and older or lower-temperature terminations, including NM-B and UF-B applications where 60°C terminal rules apply.
- 75°C – Common for modern breakers, lugs, panelboards, and many commercial or industrial terminations. THW, XHHW, USE, and SE conductors are often checked against this column when the equipment is marked for 75°C.
- 90°C – Used with high-temperature insulation such as THHN and THWN-2, XHHW-2, and RHW-2. In real installations, the 90°C value is often used for derating calculations, while the final ampacity is still limited by the terminal rating.
The Standard Conditions Behind the Numbers
Table 310.16 assumes conductors rated up to and including 2,000 volts, no more than three current-carrying conductors in the raceway or cable, and an ambient temperature of 30°C (86°F). If the jobsite is different, such as a hot attic, rooftop conduit, or crowded raceway, apply the NEC 310.15 correction and adjustment factors before final sizing. For a practical sizing check after derating, you can also use our wire size calculator.
Wire Size Amperage Chart by AWG / kcmil
The two tables below give base ampacities for copper and aluminum conductors at each temperature rating, covering common sizes from 14 AWG through 1000 kcmil. Find your gauge in the first column, then read across to the column that matches your terminal temperature rating.
Copper Ampacity
| Wire Size (AWG / kcmil) | 60°C (A) | 75°C (A) | 90°C (A) |
|---|---|---|---|
| 14 AWG | 15 | 20 | 25 |
| 12 AWG | 20 | 25 | 30 |
| 10 AWG | 30 | 35 | 40 |
| 8 AWG | 40 | 50 | 55 |
| 6 AWG | 55 | 65 | 75 |
| 4 AWG | 70 | 85 | 95 |
| 3 AWG | 85 | 100 | 115 |
| 2 AWG | 95 | 115 | 130 |
| 1 AWG | 110 | 130 | 145 |
| 1/0 AWG | 125 | 150 | 170 |
| 2/0 AWG | 145 | 175 | 195 |
| 3/0 AWG | 165 | 200 | 225 |
| 4/0 AWG | 195 | 230 | 260 |
| 250 kcmil | 215 | 255 | 290 |
| 300 kcmil | 240 | 285 | 320 |
| 350 kcmil | 260 | 310 | 350 |
| 400 kcmil | 280 | 335 | 380 |
| 500 kcmil | 320 | 380 | 430 |
| 600 kcmil | 355 | 420 | 475 |
| 700 kcmil | 385 | 460 | 520 |
| 750 kcmil | 400 | 475 | 535 |
| 800 kcmil | 410 | 490 | 555 |
| 900 kcmil | 435 | 520 | 585 |
| 1000 kcmil | 455 | 545 | 615 |
Aluminum / Copper-Clad Aluminum Ampacity
| Wire Size (AWG / kcmil) | 60°C (A) | 75°C (A) | 90°C (A) |
|---|---|---|---|
| 12 AWG | 15 | 20 | 25 |
| 10 AWG | 25 | 30 | 35 |
| 8 AWG | 35 | 40 | 45 |
| 6 AWG | 40 | 50 | 55 |
| 4 AWG | 55 | 65 | 75 |
| 3 AWG | 65 | 75 | 85 |
| 2 AWG | 75 | 90 | 100 |
| 1 AWG | 85 | 100 | 115 |
| 1/0 AWG | 100 | 120 | 135 |
| 2/0 AWG | 115 | 135 | 150 |
| 3/0 AWG | 130 | 155 | 175 |
| 4/0 AWG | 150 | 180 | 205 |
| 250 kcmil | 170 | 205 | 230 |
| 300 kcmil | 195 | 230 | 260 |
| 350 kcmil | 210 | 250 | 280 |
| 400 kcmil | 225 | 270 | 305 |
| 500 kcmil | 260 | 310 | 350 |
| 600 kcmil | 285 | 340 | 385 |
| 700 kcmil | 315 | 375 | 425 |
| 750 kcmil | 320 | 385 | 435 |
| 800 kcmil | 330 | 395 | 445 |
| 900 kcmil | 355 | 425 | 480 |
| 1000 kcmil | 375 | 445 | 500 |
Conductors larger than 1000 kcmil (1250, 1500, 1750, and 2000 kcmil) also appear in Table 310.16 for specialized high-current feeders, but they fall outside the range most projects need.
Source: NFPA 70, National Electrical Code, Table 310.16 (formerly 310.15(B)(16)), for conductors in raceway, cable, or earth at 30°C ambient with up to three current-carrying conductors. Always check them against the NEC edition adopted in your jurisdiction.
Small-gauge overcurrent limit: The 90°C column shows higher figures, but NEC 240.4(D) caps overcurrent protection on the smallest conductors regardless of insulation rating. For copper, the common limits are 14 AWG at 15A, 12 AWG at 20A, and 10 AWG at 30A. For aluminum and copper-clad aluminum, the common limits are 12 AWG at 15A and 10 AWG at 25A. Larger conductors (8 AWG and above) follow standard ampacity and breaker sizing rules. Always confirm against the code edition adopted in your jurisdiction.
How to Use the Ampacity Chart Correctly
The chart is only a starting point. Three rules turn a table value into a safe, code-compliant conductor size.
Match the Column to Your Terminal Rating
Under NEC 110.14(C), the usable ampacity is limited by the lowest-rated termination in the circuit, and that’s almost always the equipment terminal. Under 110.14(C)(1)(a), equipment rated 100A or less, or conductors 14 AWG through 1 AWG, is generally sized from the 60°C column unless the equipment is specifically listed and marked for a higher temperature. Under 110.14(C)(1)(b), equipment rated over 100A, or conductors larger than 1 AWG, generally allows the 75°C column, provided the terminals are listed and marked for 75°C. So read the temperature stamped on your breaker or lug first, then use the column that matches, or a lower one.
Where 6 AWG Copper Actually Lands
Take 6 AWG copper THHN on a 65A circuit, something we run into constantly. THHN is a 90°C insulation, so the table hands you 75A in the 90°C column, and it looks like there’s room to spare. Then you check where the wire terminates. On the 75°C lugs you find in most panels, that 6 AWG is held to 65A, so it just clears the load. Land the same wire on 60°C equipment and the ceiling comes down to 55A, and now 6 AWG falls short and you’re going up a size. Same copper, same gauge, three different ceilings, and every time it’s the weakest termination in the circuit calling the shot.
Derating for Heat and Conductor Count
When ambient temperature exceeds 30°C, multiply the table value by the correction factor in NEC 310.15(B)(1). When more than three current-carrying conductors share a raceway, apply the adjustment factor in NEC 310.15(C)(1). Both reductions stack, and you check the result against the terminal-rated column before finalizing.
Load sizing note: Ampacity is not the only sizing step. Continuous loads (those expected to run for three hours or more) generally require the conductor and overcurrent device to be rated at 125% of the load. For example, a 40A continuous load × 125% = 50A, so the conductor and overcurrent device must be sized on at least a 50A basis before any derating checks are applied. Equipment instructions, breaker ratings, and local code can all require a larger conductor than the base ampacity table alone suggests.
Quick Wire Size Reference by Breaker Amperage
This table is a fast starting point only for circuits where the terminations are confirmed 75°C-rated, there is no additional derating for ambient temperature or conductor count, and the loads are non-continuous (or have already been adjusted for the 125% continuous-load rule). It is not a substitute for a full calculation, so always verify terminal ratings, conductor type, derating, continuous-load rules, voltage drop, and local code before final sizing.
| Breaker / Circuit (A) | Copper (75°C) | Aluminum (75°C) |
|---|---|---|
| 15 A | 14 AWG | not commonly used |
| 20 A | 12 AWG | 10 AWG |
| 30 A | 10 AWG | 8 AWG |
| 40 A | 8 AWG | 8 AWG |
| 50 A | 8 AWG | 6 AWG |
| 60 A | 6 AWG | 4 AWG |
| 100 A | 3 AWG | 1 AWG |
For larger dwelling services and feeders, NEC 310.12 permits certain reduced conductor sizes, so service sizing may differ from the values above. For 60°C-rated terminals or conservative residential work, both copper and aluminum conductors may need to be upsized. The 100A row, for instance, lists 3 AWG copper, which carries 100A at 75°C but only 85A at 60°C, so a 60°C termination would push it to a larger size. Always confirm the terminal rating before relying on this quick-reference table.
Copper vs Aluminum Ampacity
Put the two charts side by side and aluminum always trails copper at the same gauge. It conducts less efficiently and sheds heat more slowly, so an aluminum run usually has to go up one or two sizes to carry what copper carries. A 50A circuit is a good example. In copper you’d start at 8 AWG, but in aluminum you’re at 6 AWG, one size larger, and you still check terminal ratings and voltage drop before you commit. We see this constantly with procurement teams who move a copper spec to aluminum to hit a budget target. It is often the right call, but when we build that cable we point out the details that keep the swap safe, the one-size step-up, the listed connectors, and the anti-oxidant compound the connector or cable manufacturer calls for. The column logic is the same for both metals, so the terminal and derating rules you would apply to copper still apply here.
Voltage Drop on Long Runs
A conductor can pass the ampacity test and still underperform over distance, because resistance bleeds off voltage along a long run. The NEC’s informational notes (210.19(A) and 215.2(A)) recommend holding branch-circuit voltage drop to about 3%, and total drop from feeder plus branch circuit to about 5%. Treat this as a design recommendation rather than a hard requirement unless a specific equipment instruction or local amendment makes it mandatory. On long feeders, ampacity sets the minimum, but voltage drop often pushes you to upsize beyond what the amp chart alone suggests, so run both checks.
A Note for International / IEC Projects
The charts above use the North American AWG/kcmil system. Projects built to IEC standards, common across Europe, the Middle East, Africa, and much of Asia, size conductors in square millimetres (mm²) and publish current-carrying capacity under IEC 60364-5-52, which uses its own installation-method tables. The physics is the same, but the reference values do not transfer directly, so don’t assume an AWG conductor’s NEC ampacity carries over to its nearest mm² size. For cross-border procurement, confirm capacity against the IEC table for your installation method, and verify which standard your specification and local authority require before ordering. This is exactly where international projects get tripped up. Having supplied both NEC/UL and IEC markets, we routinely cross-check the mm² equivalent against the correct IEC installation-method table before anything goes into production, and we can share the relevant product certifications and export references on request, so the standard behind each conductor is verifiable rather than just a claim.
Common Mistakes When Reading a Wire Ampacity Chart
- Using the 90°C column just because the wire’s insulation is rated 90°C, without checking the terminals.
- Ignoring the equipment terminal temperature rating, which usually governs the usable ampacity.
- Forgetting to derate when more than three current-carrying conductors share a raceway.
- Skipping ambient-temperature correction in hot environments such as attics or rooftops.
- Relying on ampacity alone and overlooking voltage drop on long runs.
- Assuming NEC ampacity values apply directly to IEC (mm²) installations.
FAQs
What is wire ampacity?
Ampacity is the maximum current a conductor can carry continuously, under defined conditions, without exceeding its insulation’s temperature rating.
What size wire do I need for 50 amps?
For many 75°C-rated installations, 8 AWG copper or 6 AWG aluminum is a common starting point for 50 amps. Final sizing still depends on terminal ratings, conductor type, installation conditions, continuous-load rules, and local code requirements.
Can I always use the 90°C column for THHN?
Not as the final ampacity. THHN has 90°C insulation, but you may use its 90°C value as the final allowable ampacity only if every termination is also 90°C-rated and marked. In most installations you’re limited to the 75°C or 60°C value at the terminals. The 90°C figure can still be used as the starting point for temperature-correction and conductor-count adjustment calculations where the NEC permits.
How do I adjust ampacity for high temperatures?
Multiply the table ampacity by the correction factor from NEC 310.15(B)(1) for your ambient temperature; hotter environments lower the safe current.
Which NEC edition should I follow?
Use the edition currently adopted by your local jurisdiction, since adoption dates vary by state and municipality.
Conclusion
A wire ampacity chart is only as useful as the rules applied with it. Pull the base value from NEC Table 310.16, match the temperature column to your terminal rating, derate for heat and conductor count, account for continuous loads, and check voltage drop on long runs. Nail those steps and your conductors will be both code-compliant and dependable in service.
If you’d like a hand turning that sizing into an order, ANPU Cable can help. Send us your conductor material, system voltage, load current, installation method, ambient temperature, and required standard, and we’ll help you compare suitable options across our building wire, THHN/THWN-2, and IEC cable ranges and put together a quote. Final conductor sizing should still be confirmed against your locally adopted code and a qualified professional before installation.
