If you are sizing a branch circuit or feeder, the direct answer for standard residential copper wire is: 14 AWG handles 15 amps, 12 AWG handles 20 amps, 10 AWG handles 30 amps, 8 AWG handles 40 amps, and 6 AWG handles 55 amps. However, these common values are governed by the NEC 240.4(D) small conductor rule, which artificially caps standard overcurrent protection. For larger feeders, subpanels, and commercial work, you must consult the full wire gauge amp chart based on NEC Table 310.16 to find the true thermal ampacity of the conductor.
The Master Wire Gauge Amp Chart (NEC Table 310.16)
Before pulling wire, you need to know how to read the definitive National Electrical Code (NEC) Table 310.16 (formerly 310.15(B)(16)). This table assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable. The columns are split by conductor material (Copper vs. Aluminum) and insulation temperature rating (60°C, 75°C, and 90°C). Bookmark this section for quick lookups on the most queried AWG sizes.
| AWG / kcmil | Copper 60°C | Copper 75°C | Copper 90°C | Aluminum 75°C | Aluminum 90°C |
|---|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | — | — |
| 12 AWG | 20A | 25A | 30A | — | — |
| 10 AWG | 30A | 35A | 40A | — | — |
| 8 AWG | 40A | 50A | 55A | 40A | 45A |
| 6 AWG | 55A | 65A | 75A | 50A | 55A |
| 4 AWG | 70A | 85A | 95A | 65A | 75A |
| 3 AWG | 85A | 100A | 115A | 75A | 85A |
| 2 AWG | 95A | 115A | 130A | 90A | 100A |
| 1 AWG | 110A | 130A | 145A | 100A | 115A |
| 1/0 AWG | 125A | 150A | 170A | 120A | 135A |
| 2/0 AWG | 145A | 175A | 195A | 135A | 150A |
| 3/0 AWG | 165A | 200A | 225A | 155A | 175A |
| 4/0 AWG | 195A | 230A | 260A | 180A | 205A |
Which Temperature Column Applies to Your Installation?
The most common mistake DIYers and junior electricians make when using a wire gauge amp chart is defaulting to the 90°C column because THHN/THWN-2 wire is rated for 90°C. This is incorrect for determining your final breaker size. According to industry ampacity standards and NEC 110.14(C), the allowable ampacity is dictated by the lowest temperature rating of any connected device, terminal, or conductor in the circuit.
- The 60°C Column: You must use this column for circuits rated 100 amps or less, or for conductors sized 14 AWG through 1 AWG, unless the equipment is specifically marked otherwise. Most standard residential receptacles and older breakers fall into this category.
- The 75°C Column: This applies to circuits over 100 amps, or conductors larger than 1 AWG, provided the breakers, lugs, and panels are explicitly marked with a 75°C rating (which most modern commercial and residential load centers are).
- The 90°C Column: You almost never use this column to size your final breaker. The 90°C column is reserved strictly as the starting point for derating calculations (adjusting for heat and bundling) before you apply the termination temperature limits.
How Derating Factors Modify Your Base Ampacity
The base values in the wire gauge amp chart assume optimal conditions: 30°C ambient air and no more than three current-carrying conductors in a conduit. When you deviate from this, you must apply derating factors from NEC Table 310.15(C)(1) and Table 310.15(B)(1).
Conductor Bundling Derating: When you pull multiple circuits through a single conduit, the wires heat each other up. If you have 4 to 6 current-carrying conductors in a raceway, you must multiply the base ampacity by 80%. For 7 to 9 conductors, you multiply by 70%.
Worked Example: You are pulling four 12 AWG THHN current-carrying conductors (two circuits) through a single EMT conduit to a detached garage.
1. Base ampacity from the 90°C column for 12 AWG THHN = 30A.
2. Bundling derating for 4 conductors = 80%.
3. 30A × 0.80 = 24A adjusted ampacity.
4. Because 24A is still greater than the 20A breaker protecting the circuit (and the 60°C termination limit of 20A), 12 AWG is perfectly legal and safe here. If you added a third circuit (6 current-carrying wires, 80% derating), you would still be at 24A, but if you pulled four circuits (8 wires, 70% derating), 30A × 0.70 = 21A. You would then need to upsize to 10 AWG to maintain a safe margin.
Ambient Temperature Derating: If your conduit runs across a hot roof or through a boiler room where ambient temperatures exceed 30°C (86°F), you must apply a temperature correction factor. At 41-45°C, a 90°C rated wire must be derated to 87% of its base value.
What This Wire Gauge Amp Chart Cannot Tell You
While the NEC wire gauge amp chart is the ultimate authority on thermal limits and overcurrent protection sizing, it is blind to three critical real-world installation factors.
- Voltage Drop: The chart tells you what size wire will prevent a fire, not what size wire will make your equipment run efficiently. NEC 310.15(B) includes an informational note recommending a maximum 3% voltage drop on branch circuits and 5% total for feeder and branch combined. If you are running a 240V welder 150 feet from the panel, 10 AWG might be thermally legal for 30A, but the voltage drop will exceed 5%, causing the welder to underperform and overheat. You must upsize to 8 AWG or 6 AWG strictly for distance.
- Physical Termination Limits: A 4/0 AWG aluminum feeder is rated for 200A in the 75°C column, making it the standard choice for a 200A residential service. However, the chart does not warn you that 4/0 AWG wire is incredibly stiff and may not physically bend into the tight radius of certain meter base lugs or subpanel main breakers without a specialized bending tool or a reduction to a smaller, higher-rated copper pigtail.
- Short-Circuit Withstand: Ampacity measures continuous thermal load. It does not indicate how well the wire withstands the massive magnetic and thermal forces of a 10,000-amp short circuit before the breaker clears the fault. In high-fault-current commercial environments, engineers must calculate short-circuit withstand ratings independently of the standard ampacity charts.
