If you are sizing a branch circuit or a subpanel feeder, you need a reliable gauge wire chart based on the National Electrical Code (NEC). The ampacity values below are drawn directly from NFPA 70 (NEC) Table 310.16, which dictates the allowable ampacities for insulated conductors rated up to 2000 volts. While this chart provides the baseline thermal limits of copper wire, selecting the correct wire gauge requires understanding how temperature ratings, termination limits, and environmental derating interact on the jobsite.
How to Read This AWG Gauge Wire Chart
Before pulling wire from the spool, you must understand how to read the columns in a standard NEC ampacity table. The chart below is divided into three temperature columns: 60°C, 75°C, and 90°C. These columns represent the maximum continuous current the wire can carry before its insulation begins to degrade.
Most residential breakers, receptacles, and lugs rated for 100 amps or less are only tested and listed for 60°C or 75°C terminations. Per NEC 110.14(C), even if you pull 90°C THHN wire, you must size your breaker based on the 60°C or 75°C column (whichever matches your equipment), unless the equipment is explicitly marked otherwise. The 90°C column is primarily used as a starting point for calculating derating factors.
Bookmark this section: The most queried residential sizes (14, 12, 10, 8, 6, 4, and 2 AWG) are highlighted in the table below.
| AWG Size | 60°C (140°F) TW, UF |
75°C (167°F) RHW, THHW, THW |
90°C (194°F) THHN, THWN-2, XHHW |
|---|---|---|---|
| 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 |
*Note: Per NEC 240.4(D), the overcurrent protection (breaker) for 14, 12, and 10 AWG copper is strictly limited to 15A, 20A, and 30A respectively, regardless of the higher ampacities listed in the 75°C or 90°C columns.
When Base Ampacity Isn't Enough: Derating and Temperature Adjustments
The gauge wire chart above assumes an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. In real-world installations, you must apply derating factors that modify the base 90°C value. This is where the 90°C column earns its keep.
Which column applies to your installation? You use the 90°C column to calculate the wire's adjusted ampacity after environmental penalties. However, the final derated ampacity cannot exceed the base ampacity of the 60°C or 75°C column for the purpose of sizing the termination lugs.
How derating rows modify the base value:
Let's look at a concrete jobsite example. You are wiring a 40A EV charger using 8 AWG THHN copper wire. The conduit runs through an attic that reaches 110°F (43°C), and you are pulling four current-carrying conductors (two hots, two neutrals for a multi-wire setup) in the same pipe.
- Base Ampacity: 8 AWG in the 90°C column is 55A.
- Temperature Correction: At 43°C ambient, the NEC correction factor is 0.87. (55A × 0.87 = 47.85A).
- Bundling Adjustment: For 4 to 6 current-carrying conductors, the adjustment factor is 80% (0.80). (47.85A × 0.80 = 38.28A).
Your final derated ampacity is 38.28A. Because this is below the 40A breaker you planned to use, 8 AWG is insufficient. You must step up to 6 AWG THHN (Base 75A × 0.87 × 0.80 = 52.2A) to safely protect the circuit with a 40A breaker. For a comprehensive breakdown of bundling rules, refer to the EC&M Codes and Standards archives on conductor ampacity adjustments.
What This Gauge Wire Chart Cannot Tell You
While this chart is the definitive starting point for thermal limits, it does not account for the physics of long wire runs or physical space constraints. Relying on this chart alone will lead to failures in three specific scenarios:
- Voltage Drop Over Distance: Ampacity measures heat, not voltage delivery. If you run 12 AWG wire 150 feet to a 12A landscape lighting transformer, the wire won't melt (12A is under the 20A limit), but the voltage at the load will drop below 108V, causing premature failure of the driver. For runs over 100 feet, you must calculate voltage drop using the resistance values found in NEC Chapter 9, Table 8, aiming for a maximum 3% drop on branch circuits.
- Conduit Fill Capacity: The chart tells you the wire can handle the current, but it doesn't tell you if the wires will physically fit in the pipe. Pulling four 6 AWG THHN wires into a 1/2-inch EMT conduit violates NEC Chapter 9, Table 1 (maximum 40% fill for over two wires), leading to jammed pulls and damaged insulation.
- Short-Circuit Withstand Ratings: Ampacity assumes continuous, steady-state loading. It does not indicate how the wire will survive the extreme magnetic and thermal forces of a 10,000-amp short circuit before the breaker clears the fault. This requires coordinating the wire size with the specific let-through current (I²t) of the upstream breaker or fuse.
Frequently Asked Questions About Wire Gauge Sizing
What size gauge wire do I need for a standard 20-amp breaker?
You must use a minimum of 12 AWG copper wire. While 12 AWG has a base ampacity of 25A in the 60°C column and 30A in the 90°C column, NEC 240.4(D) strictly limits the overcurrent protection for 12 AWG to 20 amps. Never use 14 AWG on a 20-amp breaker, even if the calculated load is only 12 amps; the breaker will not trip fast enough to prevent the 14 AWG wire from overheating in a fault condition.
Can I use the 90°C column for my entire circuit if I pull THHN wire?
No. THHN wire is indeed rated for 90°C, but the terminals inside your breaker panel, receptacles, and switches are typically only rated for 60°C or 75°C. Per NEC 110.14(C), the lowest temperature rating in the circuit dictates the maximum allowable ampacity for termination sizing. You use the 90°C column strictly for derating calculations (like ambient temperature and bundling), but the final adjusted ampacity must still be compared against the 60°C/75°C column limits for the breaker size.
How does aluminum wire gauge compare to copper on this chart?
Aluminum has a higher electrical resistance than copper, meaning it generates more heat at the same current. As a general rule of thumb for residential feeders, you must increase the aluminum wire size by two AWG steps compared to copper. For example, if a 100-amp subpanel feeder requires 4 AWG copper (based on the 75°C column), you must use 2 AWG aluminum (or 1/0 AL for longer runs to mitigate voltage drop). Always ensure your lugs are rated for aluminum (marked AL or CU/AL) and apply anti-oxidant paste to the terminations.
Does the equipment grounding wire need to be the same gauge as the hot wires?
Not necessarily. The equipment grounding conductor (EGC) is sized based on the rating of the overcurrent device, not the ampacity of the circuit conductors. Per NEC Table 250.122, a 20-amp circuit requires a minimum 12 AWG copper ground, a 40-amp circuit requires 10 AWG, and a 100-amp feeder requires 8 AWG. However, if you had to upsize your hot wires to compensate for voltage drop over a long distance, NEC 250.122(B) requires you to proportionally increase the size of the ground wire to maintain a low-impedance fault path.
