If you need the direct answer for standard residential branch circuits: 14 AWG wire is limited to 15 amps, 12 AWG to 20 amps, and 10 AWG to 30 amps. These limits are hard-coded by NEC 240.4(D) for overcurrent protection, regardless of the wire's insulation rating. For larger feeds, a 6 AWG copper wire handles up to 65 amps (75°C column), and 2 AWG handles 115 amps. However, picking the right wire requires understanding which temperature column actually applies to your specific breakers and terminations.
How to Read the NEC Wiring Amperage Chart
The definitive wiring amperage chart used by electricians in the United States is NEC Table 310.16 (formerly 310.15(B)(16)). This table lists the allowable ampacities of insulated conductors rated up to 2000 volts. Before you trace a row with your finger, you must understand the three temperature columns and the rules that dictate which one you are legally allowed to use.
- 20A Circuit (Outlets/Appliances): 12 AWG Copper
- 30A Circuit (Dryers/HVAC): 10 AWG Copper
- 50A Circuit (Ranges/EV Chargers): 6 AWG Copper (8 AWG is technically permitted in the 75°C column, but 6 AWG is standard practice for voltage drop and derating headroom).
- 100A Subpanel Feeder: 3 AWG Copper or 1 AWG Aluminum
- 200A Service Entrance: 2/0 AWG Copper or 4/0 AWG Aluminum
Which Column Applies to Your Installation?
The most common mistake DIYers and junior apprentices make is using the 90°C column to size their breakers. According to NEC 110.14(C), your wire sizing is limited by the lowest temperature rating of any connected component, which is almost always the breaker termination.
- 60°C Column: Applies to circuits rated 100A or less, unless the equipment is explicitly marked for 75°C. It also applies to older NM-B (Romex) cable, which is internally rated for 60°C (NEC 334.80), even if the individual conductors inside have 90°C insulation.
- 75°C Column: Applies to circuits over 100A, or circuits 100A and under where the breaker and lugs are explicitly marked "75°C" or "AL/CU". Most modern THHN/THWN-2 installations in conduit use this column for final ampacity.
- 90°C Column: You almost never use this column for final breaker sizing. The 90°C column is used exclusively as a starting point for derating calculations (adjusting for ambient heat or bundling) before you apply the 60°C or 75°C termination limit.
The Master Wiring Amperage Chart (NEC Table 310.16)
The table below details the allowable ampacities for copper conductors in a standard 30°C (86°F) ambient environment. Source standard: NFPA 70 (National Electrical Code), Table 310.16. For aluminum or copper-clad aluminum, consult the right side of the official NEC table, as aluminum requires larger gauges for the same current.
| AWG / kcmil Size | 60°C (140°F) TW, UF |
75°C (167°F) THHW, THWN, RHW |
90°C (194°F) THHN, THWN-2, XHHW |
|---|---|---|---|
| 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 | 110 |
| 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 |
*Note: Per NEC 240.4(D), the overcurrent protection (breaker size) for 14, 12, and 10 AWG copper is strictly limited to 15A, 20A, and 30A respectively, regardless of the higher values shown in the 75°C or 90°C columns.
Derating and What the Chart Cannot Tell You
The wiring amperage chart above assumes perfect conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single raceway. When real-world conditions deviate, you must apply derating factors.
How Derating Modifies the Base Value
Derating forces you to start with the 90°C column, apply a penalty multiplier, and then verify the result against your termination limits (60°C or 75°C).
- Bundling (NEC 310.15(C)(1)): If you pull 4 to 6 current-carrying conductors through a single conduit, the heat dissipation drops. You must multiply the 90°C ampacity by 80%. Example: You are pulling four 10 AWG THHN wires in a conduit for a multi-wire branch circuit. The 90°C column lists 40A. Multiplied by 80%, the derated ampacity is 32A. Since 32A is still higher than the 30A termination limit for 10 AWG, you can still use a 30A breaker. If you had 7-9 wires (70% multiplier), the math yields 28A, forcing you to upsize to 8 AWG wire.
- Ambient Temperature (NEC 310.15(B)(1)): If conduit runs across a hot roof or through an unconditioned attic where temperatures hit 46-50°C (115-122°F), you must multiply the base ampacity by a correction factor (e.g., 0.82 for 90°C wire at 50°C ambient).
What This Table Cannot Tell You
NEC Table 310.16 tells you what size wire will prevent the insulation from melting and starting a fire. It does not tell you if the wire is thick enough to deliver usable voltage to the load. For long runs (typically over 100 feet), a 10 AWG wire on a 30A circuit might be perfectly safe from a thermal perspective, but the voltage at the receptacle could drop below 114V, causing motors to overheat or electronics to brownout. The Copper Development Association recommends sizing up to maintain a maximum 3% voltage drop on branch circuits and 5% on the total feeder-to-branch run.
Furthermore, the chart does not account for continuous loads. Per NEC 210.20(A), if a load will run for 3 hours or more (like an EV charger or a commercial heater), the branch circuit rating must be 125% of the continuous load. A 32A continuous EV charger requires a 40A breaker (32 x 1.25 = 40), which dictates 8 AWG wire, even though the charger itself draws less than the 40A thermal limit of the wire.
Frequently Asked Questions
What size wire do I need for a 50 amp breaker?
For a standard 50-amp breaker (commonly used for electric ranges, large window AC units, or Level 2 EV chargers), you need 6 AWG copper wire. While the 75°C column in the chart above shows that 8 AWG is rated for exactly 50 amps, electrical best practice and many local AHJs require 6 AWG. This provides headroom for voltage drop over distance, accommodates derating if the wires share a conduit, and ensures the termination lugs do not overheat under sustained heavy loads. If you are using aluminum wire, you must step up to 4 AWG.
Can I use the 90°C column for my breaker terminations?
Almost never. NEC 110.14(C) strictly limits termination temperatures. For circuits rated 100 amps or less, you are generally bound to the 60°C column unless the breaker and equipment are explicitly stamped with a 75°C rating. For circuits over 100 amps, the 75°C column is the standard. The 90°C column is essentially a "derating buffer." You use the 90°C value to calculate your penalties for bundling or high ambient heat, but the final adjusted number must still fall within the legal limits of the 60°C or 75°C column before you can land the wire on the breaker lug.
How does bundling wires in conduit change the amperage chart?
When you bundle multiple circuits in a single conduit, the wires heat each other up, reducing their ability to dissipate thermal energy. NEC 310.15(C)(1) requires you to apply an adjustment factor to the 90°C ampacity column. If you have 4 to 6 current-carrying conductors, you multiply the 90°C ampacity by 80%. If you have 7 to 9 conductors, you multiply by 70%. Note that a neutral wire that only carries the unbalanced load from the hot wires (like in a standard 120/240V split-phase or 3-phase wye system) is not counted as a current-carrying conductor for derating purposes. However, a neutral on a multi-wire branch circuit serving non-linear loads (like modern LED drivers or computers) must be counted due to harmonic currents.
