Wire Ampacity Chart: NEC 310.16 Table
Choosing the correct wire gauge for any electrical circuit requires knowing the ampacity—the maximum current a conductor can safely carry. This guide provides a complete wire ampacity chart based on NEC Table 310.16 for both copper and aluminum conductors, covering common residential and commercial wire sizes from 14 AWG through 4/0 AWG.
What Is Wire Ampacity?
Wire ampacity is the maximum current, measured in amperes, that an electrical conductor can carry continuously without exceeding the temperature rating of its insulation. The National Electrical Code (NEC) defines ampacity in Article 100 as "the maximum current, in amperes, a conductor can carry continuously under the conditions of use without exceeding its temperature rating."
Every conductor generates heat when current flows through it. If the current exceeds the wire's rated ampacity, the insulation can degrade, melt, or catch fire. Proper ampacity selection is therefore a fundamental safety requirement in every electrical installation.
The primary source for ampacity values is NEC Table 310.16, titled "Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C Through 90°C." This table lists ampacities for copper and aluminum (or copper-clad aluminum) conductors based on three insulation temperature ratings: 60°C, 75°C, and 90°C.
Copper Wire Ampacity Chart
The table below shows the ampacity of copper conductors at an ambient temperature of 30°C (86°F), based on no more than three current-carrying conductors in a raceway or cable. Values are from NEC Table 310.16.
| Wire Gauge (AWG/kcmil) | 60°C (140°F) | 75°C (167°F) | 90°C (194°F) | Common Use |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 15A branch circuits, lighting |
| 12 AWG | 20A | 25A | 30A | 20A branch circuits, outlets |
| 10 AWG | 30A | 35A | 40A | 30A circuits, dryers, small AC |
| 8 AWG | 40A | 50A | 55A | 40A circuits, ranges, ovens |
| 6 AWG | 55A | 65A | 75A | 60A subpanels, large appliances |
| 4 AWG | 70A | 85A | 95A | 70A feeders, subpanels |
| 3 AWG | 85A | 100A | 110A | 85A feeders |
| 2 AWG | 95A | 115A | 130A | 100A service entrance |
| 1 AWG | 110A | 130A | 150A | 125A service entrance |
| 1/0 AWG | 125A | 150A | 170A | 150A service entrance |
| 2/0 AWG | 145A | 175A | 195A | 175A service entrance |
| 3/0 AWG | 165A | 200A | 225A | 200A service entrance |
| 4/0 AWG | 195A | 230A | 260A | 200A+ service entrance |
Aluminum Wire Ampacity Chart
Aluminum conductors are commonly used for service entrance cables, feeders, and larger circuits because they are lighter and less expensive than copper. However, aluminum has lower conductivity, so a larger gauge is needed to carry the same current. The following table shows aluminum conductor ampacities from NEC Table 310.16.
| Wire Gauge (AWG/kcmil) | 60°C (140°F) | 75°C (167°F) | 90°C (194°F) | Common Use |
|---|---|---|---|---|
| 12 AWG | 15A | 20A | 25A | 15A circuits (limited use) |
| 10 AWG | 25A | 30A | 35A | 25A circuits |
| 8 AWG | 30A | 40A | 45A | 30A circuits |
| 6 AWG | 40A | 50A | 55A | 50A subpanels |
| 4 AWG | 55A | 65A | 75A | 60A subpanels |
| 3 AWG | 65A | 75A | 85A | 70A feeders |
| 2 AWG | 75A | 90A | 100A | 100A service entrance |
| 1 AWG | 85A | 100A | 115A | 100A service entrance |
| 1/0 AWG | 100A | 120A | 135A | 125A service entrance |
| 2/0 AWG | 115A | 135A | 150A | 150A service entrance |
| 3/0 AWG | 130A | 155A | 175A | 175A service entrance |
| 4/0 AWG | 155A | 180A | 205A | 200A service entrance |
Understanding the Temperature Columns
NEC Table 310.16 provides three ampacity columns based on conductor insulation temperature ratings:
- 60°C (140°F): Applies to TW and UF type insulation. For 14 AWG through 10 AWG conductors, you must always use the 60°C column regardless of insulation type, because most termination points (breakers, lugs, connectors) are rated for 60°C or 75°C, and NEC 110.14(C)(1) requires using the lowest rated component.
- 75°C (167°F): Applies to THWN, THW, XHHW, and USE type insulation. For 8 AWG and larger conductors, the 75°C column is commonly used because most modern breaker terminals and equipment lugs are rated for 75°C.
- 90°C (194°F): Applies to THHN, XHHW-2, and USE-2 type insulation. The 90°C column is primarily used for derating calculations (ambient temperature correction and conductor bundling adjustments), not for direct termination ampacity.
How to Use This Chart
Follow these steps to select the correct wire gauge:
- Determine the circuit load: Calculate the total amperage of the circuit. For continuous loads (running 3+ hours), multiply by 1.25 per NEC 210.19(A)(1).
- Select the conductor material: Copper or aluminum. Copper is standard for branch circuits; aluminum is common for feeders and service entrance.
- Identify the insulation type: Match the insulation to the correct temperature column (60°C, 75°C, or 90°C).
- Apply corrections if needed: If ambient temperature exceeds 30°C or more than three current-carrying conductors are bundled together, apply derating factors from NEC 310.15(B). See our temperature derating guide.
- Choose a wire size: Select a wire gauge whose ampacity equals or exceeds the calculated load current. The breaker rating must not exceed the wire ampacity per NEC 240.4.
Small Conductor Rules: NEC 240.4(D)
The NEC has special rules for small conductors that override the general ampacity table values. Per NEC 240.4(D), overcurrent protection for 14 AWG, 12 AWG, and 10 AWG conductors is limited as follows:
| Conductor | Maximum Overcurrent Protection |
|---|---|
| 14 AWG copper | 15A |
| 12 AWG copper | 20A |
| 10 AWG copper | 30A |
| 12 AWG aluminum | 15A |
| 10 AWG aluminum | 25A |
These limits apply regardless of the insulation type or the higher ampacity values shown in the 75°C or 90°C columns. There are limited exceptions for specific applications like tap conductors and certain motor circuits.
Copper vs. Aluminum: Which to Choose?
The choice between copper and aluminum depends on several factors:
- Cost: Aluminum is significantly less expensive per foot, especially for larger gauge sizes. This makes it the preferred choice for service entrance cables and large feeders.
- Weight: Aluminum is lighter than copper, making it easier to pull through conduit for long runs.
- Ampacity: Copper carries more current per gauge size. To match a 2 AWG copper wire (115A at 75°C), you need 1/0 AWG aluminum (120A at 75°C).
- Termination: Aluminum conductors require anti-oxidant compound (penetrox) at connections and must use AL-rated connectors. Improper aluminum terminations are a known fire hazard.
- Code restrictions: Some local codes restrict aluminum for branch circuits (14–10 AWG). Always check with your local authority having jurisdiction (AHJ).
Common Applications by Wire Size
| Circuit Application | Copper Wire | Breaker Size |
|---|---|---|
| Lighting circuits | 14 AWG | 15A |
| General outlets, kitchen, bath | 12 AWG | 20A |
| Window AC, small appliances | 10 AWG | 30A |
| Electric dryer, range | 8 AWG | 40A |
| Central AC (3-ton), subpanel | 6 AWG | 60A |
| Large subpanel, pool equipment | 4 AWG | 70A |
| 100A service or subpanel | 2 AWG copper / 1/0 AWG aluminum | 100A |
| 200A service entrance | 3/0 AWG copper / 4/0 AWG aluminum | 200A |
Ambient Temperature Considerations
The ampacity values in NEC Table 310.16 are based on an ambient temperature of 30°C (86°F). When wires are installed in environments that exceed this temperature—such as attics, near furnaces, or in industrial settings—the ampacity must be reduced using the correction factors in NEC Table 310.15(B)(2). For example, in an attic that reaches 50°C (122°F) in summer, a 12 AWG copper wire rated at 20A may need to be derated to approximately 15A, requiring a step up to 10 AWG. See our temperature derating factors guide for the complete correction table.
Conductor Bundling Derating
When more than three current-carrying conductors are installed in a raceway or cable, they must be derated per NEC 310.15(B)(3)(a). The more conductors bundled together, the more heat they generate, and the lower the allowable ampacity. Bundling derating factors are:
- 4–6 conductors: 80% of table ampacity
- 7–9 conductors: 70% of table ampacity
- 10–20 conductors: 50% of table ampacity
These factors can significantly impact wire selection, especially in conduit runs with multiple circuits.
When to Use a Wire Size Calculator
While ampacity charts are useful for quick reference, real-world installations often involve multiple correction factors—ambient temperature, conductor bundling, voltage drop over long distances, and special NEC rules for equipment. A dedicated calculator handles these variables simultaneously. Our Wire Size Calculator accounts for all NEC 310.16 requirements, temperature corrections, and voltage drop to recommend the optimal wire gauge for any installation.
Frequently Asked Questions
What is wire ampacity?
Wire ampacity is the maximum amount of electrical current a conductor can carry continuously without exceeding its temperature rating. It is determined by NEC Table 310.16 and depends on conductor material, insulation type, and ambient temperature.
What ampacity does 12 AWG copper wire have?
12 AWG copper wire has an ampacity of 20 amperes at 60°C insulation rating (THHN, THWN) in a 30°C ambient environment per NEC Table 310.16. This makes it the standard wire for 20-amp branch circuits.
How does aluminum wire ampacity compare to copper?
Aluminum conductors have lower ampacity than copper of the same gauge. For example, 12 AWG aluminum is rated 15A vs 20A for copper at 60°C. To match copper ampacity, aluminum wire must be one or two sizes larger.
What is the difference between 60°C, 75°C, and 90°C ampacity columns?
The temperature columns in NEC Table 310.16 correspond to the insulation rating of the wire. Higher-rated insulation allows higher ampacity. However, for 14–10 AWG conductors, the 60°C column must always be used regardless of insulation, per NEC 110.14(C)(1).
Can I use a higher ampacity value if my wire has 90°C insulation?
For 8 AWG and larger, you may use the 75°C column if the termination points are rated for 75°C (most breakers and lugs are). The 90°C column is primarily used for derating calculations, not direct termination ampacity.