When you are standing in the electrical aisle staring at spools of NM-B (Romex) and THHN, the numbers printed on the insulation jacket do not tell the whole story. The definitive amperage AWG chart—formally known as NEC Table 310.16—dictates the maximum continuous current a specific wire gauge can carry before its insulation begins to thermally degrade. For the most common residential branch circuits, the baseline answers are: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps. However, those numbers only apply under specific installation conditions. If you are pulling wire through a hot attic or bundling multiple circuits in a single conduit, the base chart values will lead you to undersized wire and tripped breakers.
How to Read the NEC Ampacity Chart (and Which Column to Use)
The most common mistake DIYers and junior apprentices make with the amperage AWG chart is looking at the highest number in the row and assuming that is the wire's absolute limit. The chart is divided into temperature columns—typically 60°C, 75°C, and 90°C—which correspond to the thermal rating of the wire's insulation and the equipment terminations it connects to.
Here is how to read the columns based on your installation method:
- 60°C Column: Use this for NM-B (Romex) cable, as the jacket limits heat dissipation. You must also use this column for 14, 12, and 10 AWG wires terminating on standard 15A, 20A, and 30A breakers, regardless of the wire's insulation rating.
- 75°C Column: Use this for larger feeder wires (8 AWG and larger) terminating on standard 75°C-rated breakers, or for THHN/THWN wires in conduit terminating on 75°C equipment.
- 90°C Column: You almost never use this column for final breaker sizing. The 90°C column is strictly used as the starting base value when you need to calculate derating adjustments for conduit fill or high ambient temperatures.
The Complete Amperage AWG Chart (NEC Table 310.16)
The following data is extracted from NEC Table 310.16 (2020/2023 editions) for ambient temperatures of 30°C (86°F). It covers the most frequently used copper and aluminum sizes in residential and light commercial work.
| AWG / kcmil Size | 60°C Copper (NM-B / Romex) | 75°C Copper (THHN in Conduit) | 90°C Copper (THHN-2 Base) | 75°C Aluminum (XHHW) |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A | — |
| 12 AWG | 20 A | 25 A | 30 A | — |
| 10 AWG | 30 A | 35 A | 40 A | — |
| 8 AWG | 40 A | 50 A | 55 A | 40 A |
| 6 AWG | 55 A | 65 A | 75 A | 50 A |
| 4 AWG | 70 A | 85 A | 95 A | 65 A |
| 3 AWG | 85 A | 100 A | 115 A | 75 A |
| 2 AWG | 95 A | 115 A | 130 A | 90 A |
| 1 AWG | 110 A | 130 A | 145 A | 100 A |
| 1/0 AWG | 125 A | 150 A | 170 A | 120 A |
| 2/0 AWG | 145 A | 175 A | 195 A | 135 A |
| 3/0 AWG | 165 A | 200 A | 225 A | 155 A |
| 4/0 AWG | 195 A | 230 A | 260 A | 180 A |
Source: NFPA 70 National Electrical Code, Table 310.16. Always verify against your local AHJ's adopted code year, as minor adjustments occur between cycles.
Bookmark-Friendly Quick-Jump Rows
For the most common heavy-load queries, here is your shortcut:
- For a 50-Amp Breaker (Hot Tub / EV Charger): Use 6 AWG Copper (75°C column) or 4 AWG Aluminum. If using NM-B cable, 6 AWG is rated for 55A in the 60°C column, which is sufficient for a 50A load.
- For a 100-Amp Breaker (Subpanel Feeder): Use 3 AWG Copper or 1 AWG Aluminum. (Many installers use 2 AWG Aluminum, which is rated 90A; this is only permitted if the calculated continuous load is strictly under 90A, otherwise you must step up to 1 AWG).
- For a 200-Amp Breaker (Main Service Entrance): Use 2/0 AWG Copper or 4/0 AWG Aluminum.
What This Amperage AWG Chart Cannot Tell You (Derating & Edge Cases)
The chart above assumes ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. In the real world, you must apply adjustment factors that modify the base value.
Conduit Fill Derating (NEC 310.15(C)(1))
When you pull more than three current-carrying wires through a single raceway, they heat each other up. You must apply a derating multiplier to the 90°C column base value. For example, if you have four current-carrying 12 AWG THHN wires in a conduit, the derating factor is 80%. You take the 90°C base ampacity for 12 AWG (30A) and multiply it by 0.80, resulting in a derated ampacity of 24A. Because 24A is still above the 20A breaker size, you can still protect the circuit with a 20A breaker. However, if you had 10 wires in that conduit (50% derating), 30A x 0.50 = 15A, meaning you could no longer use 12 AWG on a 20A breaker.
Ambient Temperature Correction
If your conduit runs across a 110°F attic or on a rooftop, the wire cannot dissipate heat as effectively. You must multiply the base ampacity by a temperature correction factor found in the bottom of NEC Table 310.16. Industry resources like EC&M frequently highlight that ignoring ambient temperature in hot climates is a leading cause of nuisance breaker trips and premature insulation failure.
Voltage Drop Limitations
The amperage AWG chart only tells you the thermal limit of the wire; it tells you absolutely nothing about voltage drop. If you are running a 50-amp circuit to a detached garage 150 feet away, 6 AWG copper will keep the wire from melting, but the voltage at the far end will sag below 110V under load, potentially damaging motors or electronics. For long runs, you must upsize the wire to maintain a maximum 3% voltage drop, often requiring you to jump two or three sizes larger than the chart dictates.
Amperage AWG Chart FAQ
What size wire do I need for a 50 amp breaker?
For a standard 50-amp circuit (like a welder, hot tub, or Level 2 EV charger), you need 6 AWG copper wire if you are using THHN in conduit (rated 65A at 75°C) or NM-B Romex (rated 55A at 60°C). If you are using aluminum wire, you must step up to 4 AWG (rated 65A at 75°C). Note that if the run exceeds 60-80 feet, you should upsize to 4 AWG copper or 2 AWG aluminum to mitigate voltage drop.
Can I use the 90°C column for my home wiring breaker terminations?
No. While you can buy 90°C-rated wire (like THHN-2), NEC 110.14(C) strictly limits the final ampacity to the lowest temperature rating of the connected equipment. Almost all residential breakers and receptacles are rated for 75°C maximum. Furthermore, for circuits 100A and under, the code mandates using the 60°C column for final sizing. You only use the 90°C column as a mathematical starting point to calculate derating adjustments before checking if the final adjusted number still meets the 60°C or 75°C requirement.
How does voltage drop change the AWG size on this chart?
The amperage AWG chart is purely a thermal safety table; it does not account for the resistance of the wire over distance. According to Copper Development Association guidelines, a voltage drop exceeding 3% on a branch circuit is considered poor design. If you are running a 20-amp circuit 120 feet to a shed, the chart says 12 AWG is fine thermally. But 12 AWG copper over 240 feet of total circuit length (hot + neutral) will drop nearly 4% of your voltage at full load. To fix this, you would ignore the chart's minimum and upsize to 10 AWG or even 8 AWG to ensure your tools receive a solid 120V.
