The AWG ampacity chart dictates the maximum continuous current a conductor can carry before its insulation begins to thermally degrade. For residential and commercial branch circuits in the US, the definitive source is NEC Table 310.16 (published by the NFPA). While you can buy wire at any hardware store, picking the wrong gauge or misreading the temperature columns can result in tripped breakers, melted terminal lugs, or a failed inspection.
This reference guide provides the complete copper ampacity table, explains exactly which temperature column applies to your termination points, and breaks down the derating math you need when pulling multiple circuits through a single conduit.
How to Read the AWG Ampacity Chart (And Which Column Applies)
The most common mistake DIYers and junior apprentices make is looking at the 90°C column because modern THHN wire is rated for it, and then sizing their breaker to that higher number. Do not do this.
To use the chart correctly, you must understand the three temperature columns:
- 60°C Column: Used for older insulation types (TW, UF-B) and specific equipment explicitly marked for 60°C. You must also use this column for 14, 12, and 10 AWG wires due to NEC 240.4(D) small-conductor rules, regardless of the wire's actual insulation rating.
- 75°C Column: This is your baseline for breaker sizing. Almost all modern residential breakers, panel lugs, and receptacle terminals are rated for 75°C. Even if you pull 90°C THHN wire, the termination point is the weakest link. You must size your overcurrent protection based on the 75°C ampacity.
- 90°C Column: Used only as the starting baseline for derating calculations (adjusting for heat and bundling) before comparing the result back to the 75°C termination limits.
The most queried sizes for standard 120V/240V branch circuits are 14 AWG (15A), 12 AWG (20A), 10 AWG (30A), 8 AWG (40A/50A), and 6 AWG (55A/65A). Keep these rows in mind when planning standard receptacle, dryer, and range circuits.
NEC Table 310.16: Copper Conductors (Ampacities)
Source Standard: NFPA 70, National Electrical Code (NEC) Table 310.16 (2023 Edition). Based on an ambient temperature of 30°C (86°F).
| AWG / kcmil | 60°C (140°F) TW, UF |
75°C (167°F) RHW, THHW, THW |
90°C (194°F) THHN, THWN-2 |
|---|---|---|---|
| 14 | 15 | 20 | 25 |
| 12 | 20 | 25 | 30 |
| 10 | 30 | 35 | 40 |
| 8 | 40 | 50 | 55 |
| 6 | 55 | 65 | 75 |
| 4 | 70 | 85 | 95 |
| 3 | 85 | 100 | 115 |
| 2 | 95 | 115 | 130 |
| 1 | 110 | 130 | 145 |
| 1/0 | 125 | 150 | 170 |
| 2/0 | 145 | 175 | 195 |
| 3/0 | 165 | 200 | 225 |
| 4/0 | 195 | 230 | 260 |
For authoritative code references, always consult the latest NFPA National Electrical Code or verified educational resources like Electrical Construction & Maintenance (ECM).
Derating Factors: How Bundling and Temperature Modify Base Values
The ampacities in the table above assume two things: an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors (CCCs) bundled together in a single conduit or cable. When you violate either assumption, the wire cannot shed heat as efficiently, and you must apply derating factors from NEC Table 310.15(C)(1).
Here is the golden rule of derating: You always start your derating math using the 90°C column, regardless of your termination ratings. Once you calculate the derated ampacity, you compare it to the 75°C column, and use the lower of the two numbers to size your breaker.
Worked Numeric Example: Bundled THHN in Conduit
Imagine you are pulling four separate 120V circuits through a single 3/4-inch EMT conduit. That gives you 4 hot wires and 4 neutral wires, totaling 8 current-carrying conductors (grounds do not count as CCCs).
- Identify Base Ampacity: 12 AWG THHN in the 90°C column is 30A.
- Find the Derating Factor: NEC Table 310.15(C)(1) states that for 7 to 9 CCCs, the adjustment factor is 70%.
- Calculate Derated Ampacity: 30A × 0.70 = 21A.
- Final Sizing: Compare 21A to the 75°C column for 12 AWG (which is 25A). The lower number is 21A. Since 21A is greater than your 20A breaker, 12 AWG THHN is still legal and safe for a 20A circuit in this bundled scenario.
What the AWG Ampacity Chart Cannot Tell You
While Table 310.16 is the bible for thermal limits, it is not a complete design tool. Relying on it blindly will cause failures in three specific edge cases:
- Voltage Drop: The chart tells you what the wire can handle thermally, not what it will deliver electrically. A 14 AWG wire on a 15A breaker is legally compliant for a 100-foot run to a shed, but the voltage drop will exceed 5%, causing motors to stall and lights to dim. For runs over 50 feet, use Chapter 9, Table 8 resistance data to calculate voltage drop and upsize the wire accordingly.
- Conduit Fill Capacity: Just because 12 AWG wire can carry the current doesn't mean you can physically fit twenty of them into a 1/2-inch conduit. You must cross-reference NEC Chapter 9, Table 1 to ensure you aren't exceeding 40% conduit fill, which prevents wire jamming and insulation tearing during pulls.
- Short-Circuit Withstand Ratings: Ampacity deals with continuous, steady-state heat. It does not tell you if the wire can survive the massive magnetic and thermal forces of a 10,000A short circuit before the breaker trips. For high-fault-current environments (like main service feeders), you must verify the wire's short-circuit withstand rating against the breaker's let-through current data.
AWG Ampacity Chart FAQ
What size breaker do I use for 8 AWG wire according to the ampacity chart?
Assuming standard copper THHN and 75°C rated terminals, the 75°C column lists 8 AWG at 50 Amps. Therefore, you can protect 8 AWG copper wire with a 50A breaker. A common misconception is that 8 AWG is capped at 40A; however, NEC 240.4(D) small-conductor rules strictly cap 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A), but they do not restrict 8 AWG. If your specific equipment (like an older HVAC disconnect) is strictly marked for 60°C, you must drop down to the 60°C column, limiting 8 AWG to 40A.
Why does the NEC ampacity chart show 90°C ratings if my breaker is only 75°C?
The 90°C column exists primarily to give installers mathematical 'headroom' for derating. When you bundle wires in a conduit or run them through a hot attic (ambient temperature correction), you must reduce the wire's ampacity. By starting the math at the higher 90°C baseline, the derated value often remains high enough to safely terminate on standard 75°C breakers and lugs without forcing you to upsize to a thicker, more expensive wire gauge.
Does the AWG ampacity chart apply to aluminum wire in residential subpanels?
Yes, but you must use the Aluminum columns in NEC Table 310.16, not the copper columns shown above. Aluminum has higher electrical resistance, meaning you generally need to jump up two AWG sizes to match copper's ampacity. For example, to feed a 90A subpanel, you would use 3 AWG Copper, but you must use 2 AWG Aluminum. When using aluminum, always apply anti-oxidant compound (like Noalox) to the stripped ends and use a calibrated torque screwdriver to tighten the panel lugs to the manufacturer's exact inch-pound specification to prevent thermal creep and arcing over time.
