The AWG cable current rating (ampacity) is the maximum continuous current a conductor can carry without exceeding its insulation temperature limits. For standard residential copper wire, the baseline ratings are: 14 AWG (15A), 12 AWG (20A), 10 AWG (30A), 8 AWG (40A), 6 AWG (65A), and 4 AWG (85A). However, these numbers are only the starting point. Your actual allowable current depends entirely on the insulation type, the temperature rating of your termination points, and how many wires are bundled together in a raceway.
This reference guide provides the complete NFPA 70 (NEC) Table 310.16 data for copper conductors, explains exactly which temperature column applies to your specific installation, and breaks down the derating math required for conduit runs.
How to Read the NEC Ampacity Table
Before looking at the numbers, you must understand the three temperature columns in the NEC ampacity tables. The insulation on modern wire (like THHN) is typically rated for 90°C, but you are rarely allowed to use the full 90°C ampacity for the final circuit sizing.
- 60°C Column: Mandatory for 14, 12, and 10 AWG conductors, regardless of insulation type (NEC 240.4(D)). Also applies when using NM-B (Romex) cable, as the overall cable assembly is limited to 60°C.
- 75°C Column: Used for most commercial and residential terminations. If your breaker lugs and receptacles are rated 75°C (standard for modern 100A+ panels), you use this column for wires 8 AWG and larger.
- 90°C Column: Used only as the base starting number for derating calculations (ambient temperature adjustments and conduit fill bundling). The final derated ampacity must then be compared to the termination limit (60°C or 75°C), and you must use the lower of the two values.
What the Table Cannot Tell You
The NEC ampacity table is strictly a thermal limit chart. It tells you when the wire will melt or degrade. It does not tell you:
- Voltage Drop: A 14 AWG wire can safely carry 15A thermally, but pushing 15A through 150 feet of 14 AWG will result in severe voltage drop, causing motors to overheat and lights to dim. Always calculate voltage drop for runs over 100 feet.
- Short-Circuit Withstand: Ampacity assumes continuous, steady-state loading. It does not account for the magnetic and thermal forces of a 10,000A short-circuit event (which is handled by breaker AIC ratings and wire bracing).
- Physical Terminal Fit: A 250 kcmil wire might have the right ampacity, but it may physically fail to bend into a standard 200A panel lug without specialized offset tools.
Master AWG Cable Current Rating Chart (NEC Table 310.16)
The following table lists the allowable ampacities for insulated copper conductors rated 0-2000 volts, based on an ambient temperature of 30°C (86°F).
Bookmark Quick-Jumps: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG
| AWG Size / kcmil | 60°C (140°F) NM-B / Small Wire |
75°C (167°F) Standard Terminations |
90°C (194°F) THHN / Derating Base |
|---|---|---|---|
| 14 AWG | 15A | 20A* | 25A* |
| 12 AWG | 20A | 25A* | 30A* |
| 10 AWG | 30A | 35A* | 40A* |
| 8 AWG | 40A | 50A | 55A |
| 6 AWG | 55A | 65A | 75A |
| 4 AWG | 70A | 85A | 95A |
| 2 AWG | 95A | 115A | 130A |
| 1 AWG | 110A | 130A | 145A |
| 1/0 AWG | 125A | 150A | 170A |
| 2/0 AWG | 145A | 175A | 195A |
| 3/0 AWG | 165A | 200A | 225A |
| 4/0 AWG | 195A | 230A | 260A |
*Note: While the 75°C and 90°C columns show higher values for 14, 12, and 10 AWG, NEC 240.4(D) strictly limits the overcurrent protection for these small conductors to 15A, 20A, and 30A respectively, effectively locking them to the 60°C column for standard branch circuits.
Derating: When the Base Rating Isn't Enough
The numbers in the chart above assume two things: an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors bundled together. When you violate either assumption, the wire cannot dissipate heat as efficiently, and you must derate the AWG cable current rating.
Derating is calculated using the 90°C column, even if your terminations are only rated for 75°C. You multiply the 90°C base ampacity by the derating factor found in NEC Table 310.15(C)(1) for bundling, or Table 310.15(B)(1) for ambient temperature. After doing the math, you compare your result to the termination column limit, and the lowest number wins.
Worked Example: Bundled THHN in Conduit
Imagine you are pulling four 12 AWG THHN copper wires (two hot, one neutral, one ground) through a conduit to a 20A receptacle in a garage.
- Identify current-carrying conductors: The two hots and the neutral count. The ground does not. That's 3 current-carrying conductors. No bundling derating is required. (If you had two circuits, making 4 current-carrying wires, you would apply an 80% derating factor: 30A x 0.80 = 24A).
- Check ambient temperature: If the garage attic space reaches 110°F (43°C), you must apply the 90°C ambient temperature correction factor of 0.87.
- Do the math: 12 AWG at 90°C is 30A. 30A × 0.87 = 26.1A.
- Compare to terminations: The receptacle termination limit (60°C column for 12 AWG) is 20A.
- Final Verdict: The lowest value is 20A. You can still use a 20A breaker, but you are right at the limit. If the attic hit 130°F, the derated value would drop below 20A, forcing you to upsize to 10 AWG.
For complex commercial runs, always consult the latest EC&M NEC guidelines or use a verified voltage drop and derating calculator from manufacturers like Southwire to ensure compliance.
Frequently Asked Questions
What is the AWG cable current rating for a 50-amp circuit?
For a standard 50-amp circuit (like an EV charger or electric range), you must use 6 AWG copper wire. While 8 AWG copper has a 75°C ampacity of 50A, NEC 240.4(D) and general termination sizing rules heavily favor 6 AWG (rated 65A at 75°C) to ensure the breaker lugs can physically accept the wire and to provide a buffer for voltage drop on longer runs. If using aluminum, you must step up to 4 AWG.
Can I use the 90°C ampacity column for my whole circuit?
No. Almost no residential or commercial breakers, lugs, or receptacles are rated for 90°C terminations. NEC 110.14(C) dictates that you must size your wire based on the lowest temperature rating of any connected component. Since most standard equipment is rated 75°C (and smaller wires default to 60°C), the 90°C column is strictly a mathematical starting point for derating calculations, not a final allowable ampacity.
Does the AWG current rating change for aluminum wire?
Yes, aluminum has higher electrical resistance than copper, resulting in lower ampacities for the same physical gauge. For example, 2 AWG copper is rated for 115A (75°C column), while 2 AWG aluminum is only rated for 90A. When sizing aluminum feeders for subpanels or service entrances, you must consult the aluminum-specific columns in NEC Table 310.16, and you must use anti-oxidant paste (like Noalox) on all terminations to prevent galvanic corrosion and high-resistance heating.
How does voltage drop affect my AWG cable current rating?
Ampacity and voltage drop are two completely different physics problems. Ampacity is about heat dissipation (preventing the insulation from melting). Voltage drop is about performance (ensuring the load receives enough voltage to operate correctly). A 10 AWG wire might be perfectly safe carrying 30A over 200 feet from a thermal perspective, but the voltage at the end of the run might drop to 105V, which will burn out an AC compressor motor. Always upsize your wire gauge for runs exceeding 100 feet to keep voltage drop under 3% for branch circuits.
