If you need the standard amp gauge wire chart values for residential and light commercial copper wiring, here is the direct answer: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, 10 AWG for 30 amps, 8 AWG for 40 amps, and 6 AWG for 55 amps. These baseline numbers assume copper conductors, a maximum of three current-carrying conductors in a raceway, and an ambient temperature of 30°C (86°F).
However, simply matching the breaker to the wire's maximum thermal limit is a fast track to a failed inspection or a melted terminal lug. The numbers above are derived from the National Electrical Code (NEC) Table 310.16, but applying them correctly requires understanding which temperature column your specific installation falls under and how bundling wires in a conduit derates those baseline values.
The Master Amp Gauge Wire Chart (NEC Table 310.16)
The table below is the definitive reference for copper wire ampacity. Before you pull wire, you need to know how to read it. The NEC publishes ampacity across three temperature columns: 60°C, 75°C, and 90°C. These columns do not represent the ambient temperature of your room; they represent the maximum temperature the wire's insulation and the connected terminals can safely withstand without degrading.
- 15A Circuit: 14 AWG (60°C column)
- 20A Circuit: 12 AWG (60°C column)
- 30A Circuit: 10 AWG (60°C column)
- 40A Circuit: 8 AWG (60°C column)
- 50A Circuit: 6 AWG (75°C column)
- 100A Feeder: 3 AWG (75°C column)
| Wire Size (AWG/kcmil) | 60°C Column (140°F) | 75°C Column (167°F) | 90°C Column (194°F) |
|---|---|---|---|
| 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 |
| 3 AWG | 85A | 100A | 115A |
| 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 |
Which Column Applies to Your Installation (and Derating Rules)
The most common mistake DIYers and junior apprentices make is looking at the 90°C column because modern THHN/THWN-2 wire is rated for 90°C. You almost never use the 90°C column for final breaker sizing.
According to NEC 110.14(C) terminal temperature limitations, the ampacity of a circuit is limited by the lowest temperature rating of any connected component. Most standard residential circuit breakers and receptacles are rated for 75°C terminals. However, NEC 110.14(C)(1)(a) explicitly states that for circuits rated 100 amps or less, or using 14 AWG through 1 AWG wire, you must use the 60°C column unless the equipment is specifically tested and marked for 75°C. Furthermore, if you are using NM-B (Romex) cable, NEC 334.80 mandates that the ampacity must be based on the 60°C column, regardless of the fact that the internal THHN conductors have 90°C insulation.
When do you use the 90°C column? Only for derating calculations. If you have to derate wire due to high ambient temperatures or bundling multiple conductors in a single conduit, you apply the derating percentage to the 90°C base value, and then compare that result to the 60°C or 75°C termination limit. The final breaker size cannot exceed the termination limit.
How Derating Modifies the Base Value
When you pull more than three current-carrying conductors through a single conduit, the wires heat each other up. The NEC requires you to reduce (derate) the wire's ampacity to prevent the insulation from melting inside the pipe. Note that grounding wires do not count as current-carrying, but in a multi-wire branch circuit (MWBC), the shared neutral does count.
| Number of Conductors in Conduit | Derating Multiplier | Example: 10 AWG THHN (90°C base = 40A) |
|---|---|---|
| 1 to 3 | 100% | 40A (No derating applied) |
| 4 to 6 | 80% | 32A (Next standard breaker: 30A) |
| 7 to 9 | 70% | 28A (Next standard breaker: 25A) |
| 10 to 20 | 50% | 20A (Next standard breaker: 20A) |
What This Chart Cannot Tell You (Edge Cases and Code Limits)
An amp gauge wire chart is a thermal limit reference, not a complete design tool. Relying on it blindly ignores three critical physical and legal realities of electrical installations.
1. The Small Conductor Rule (NEC 240.4(D))
Look at the 90°C column for 12 AWG wire: it says 30A. Why, then, can you not put 12 AWG wire on a 30A breaker? NEC 240.4(D) places hard, overridable limits on small conductors to protect them from high-fault-current events that could melt the wire before the breaker's magnetic trip engages. Regardless of the insulation type or temperature column, the maximum overcurrent protection is strictly capped:
- 14 AWG: Maximum 15 Amps
- 12 AWG: Maximum 20 Amps
- 10 AWG: Maximum 30 Amps
There are specific exceptions for motor circuits and HVAC equipment where inrush currents require larger breakers, but for standard branch circuits, these caps are absolute.
2. Voltage Drop Over Distance
Table 310.16 assumes a relatively short wire run. It tells you the wire won't catch fire at 55 amps on 6 AWG, but it doesn't tell you what the voltage will be at the receptacle 150 feet away. On long runs, resistance causes voltage drop. A 3% drop on a 120V branch circuit is acceptable (dropping to 116.4V), but a 10% drop will cause motors to overheat and lights to dim.
For example, pulling 15 amps continuously on a 100-foot run of 14 AWG copper results in roughly a 4.6V drop (3.8%), which is borderline. If your run exceeds 50 feet for a heavily loaded 15A or 20A circuit, bump up one wire size (e.g., use 12 AWG on a 15A circuit) strictly to mitigate voltage drop, even though the 14 AWG is legally permitted for the ampacity.
3. Continuous vs. Non-Continuous Loads
The ampacities in the chart assume a mix of loads. If a load is expected to run at maximum current for three hours or more (like a commercial lighting circuit, a server rack, or an EV charger), the NEC defines it as a continuous load. You must derate the breaker and wire capacity by 125%. Therefore, a 20A continuous load requires a wire and breaker sized for 25A (20A x 1.25). You would need to step up to 10 AWG wire (rated 30A at 60°C) and a 30A breaker, because a 12 AWG wire on a 20A breaker can only safely handle 16A of continuous draw (20A / 1.25).
Always treat the amp gauge wire chart as your starting point for thermal safety, then filter the result through termination limits, conduit fill adjustments, and continuous load multipliers before finalizing your breaker size.
