When you are pulling wire for a new subpanel, wiring a 240V dryer outlet, or extending a 15A lighting circuit, guessing the wire size is a fast track to melted insulation or a failed inspection. The direct answer for standard residential copper branch circuits is straightforward: 14 AWG handles 15 amps, 12 AWG handles 20 amps, 10 AWG handles 30 amps, and 8 AWG handles 40 amps (based on the 60°C termination column). But once you step into larger feeders, aluminum conductors, or conduit with multiple wires, you need the complete wire AWG chart governed by NEC Table 310.16.
How to Read the NEC Wire AWG Chart
The most common mistake DIYers and junior apprentices make with an ampacity table is looking at the wrong temperature column. The National Electrical Code (NEC) publishes ampacities for 60°C, 75°C, and 90°C insulation types. However, which column applies to your installation is dictated by NEC 110.14(C) termination provisions, not just the wire's insulation rating.
- 60°C Column: Must be used for circuits rated 100A or less, or for conductors sized 14 AWG through 1 AWG. This applies to most standard residential branch circuits (NM-B Romex, standard receptacles, and lighting switches) because the termination lugs are typically only rated for 60°C.
- 75°C Column: Used for circuits rated over 100A, or conductors larger than 1 AWG. This applies to main service panels, large subpanel feeders, and heavy appliance circuits where the equipment lugs are explicitly marked 75°C.
- 90°C Column: This column is only used as the starting base value for derating calculations (ambient temperature or conduit bundling). You cannot use the 90°C ampacity to size your breaker, even if you are using THHN wire rated for 90°C.
Bookmark Quick-Jump (Copper, 60°C Column): 14 AWG = 15A | 12 AWG = 20A | 10 AWG = 30A | 8 AWG = 40A | 6 AWG = 55A | 4 AWG = 70A | 2 AWG = 95A
Below is the complete reference chart for copper conductors. Source: NEC Table 310.16 (2023/2026 Editions), assuming an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway. For deeper code context, refer to the NFPA 70 National Electrical Code documentation.
| AWG / kcmil | 60°C (TW, UF) | 75°C (THHW, THWN) | 90°C (THHN, THWN-2) |
|---|---|---|---|
| 14 | 15A * | 20A * | 25A * |
| 12 | 20A * | 25A * | 30A * |
| 10 | 30A * | 35A * | 40A * |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 115A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
* Note: Per NEC 240.4(D), the maximum overcurrent protection for 14, 12, and 10 AWG copper is strictly capped at 15A, 20A, and 30A respectively, regardless of the 75°C or 90°C column values.
Derating Factors and What the Chart Cannot Tell You
The ampacities listed above assume ideal conditions: an ambient temperature of 30°C (86°F) and a maximum of three current-carrying conductors bundled together. When conditions change, how derating rows modify the base value becomes critical to prevent a fire.
Derating is calculated using the 90°C column for THHN/THWN-2 wire, applying the adjustment factors from NEC Table 310.15(C)(1). Let's look at a real-world bench example: You are pulling four current-carrying conductors (two 120V circuits sharing a neutral, plus a dedicated 240V circuit) through a single EMT conduit.
- Base Value: 12 AWG THHN in the 90°C column is rated for 30A.
- Derating Factor: 4 to 6 current-carrying conductors requires an 80% adjustment factor.
- Calculation: 30A × 0.80 = 24A.
- Final Sizing: 24A is still greater than the 20A breaker limit for 12 AWG (per 240.4(D)), so 12 AWG is perfectly legal and safe here.
What the table cannot tell you: The wire AWG chart assumes short, standard-length runs. It does not account for voltage drop. If you are running a 120V circuit 150 feet to a detached garage workshop, a 14 AWG wire carrying 12A will experience a voltage drop exceeding 5%, causing motors to overheat and LED drivers to fail early. For runs over 100 feet, always calculate voltage drop and upsize your wire accordingly, even if the breaker size doesn't strictly require it.
Wire AWG Chart FAQ
What size wire do I need for a 50 amp breaker?
For a standard 50A circuit (like an EV charger or a workshop welder outlet), you need 6 AWG copper wire if the equipment terminations are rated for 75°C (which yields 65A in the chart, safely above the 50A requirement). If you are using aluminum wire (like SER cable for a subpanel feeder), you must step up to 4 AWG aluminum, as aluminum has a lower ampacity per cross-sectional area. If the 50A breaker lugs are strictly rated for 60°C, you must use 4 AWG copper (rated 70A at 60°C).
Can I use the 90°C column to size my residential breakers?
No. This is one of the most common code violations seen in residential rough-ins. Even though the THHN wire you buy at the hardware store is printed with '90°C', NEC 110.14(C) dictates that the ampacity of the circuit is limited by the lowest temperature rating of any connected termination, device, or conductor. Standard residential breakers, receptacles, and switches are rated for 60°C or 75°C. Therefore, your final breaker size must be based on the 60°C or 75°C columns. The 90°C column is exclusively a mathematical starting point for calculating derating adjustments.
How does voltage drop change my wire AWG size selection?
The NEC recommends a maximum voltage drop of 3% for branch circuits and 5% overall (feeder plus branch). The wire AWG chart does not factor in distance. For example, if you are wiring a 20A, 120V receptacle 120 feet away from the panel, using the standard 12 AWG copper will result in a 4.1V drop (3.4%). To keep the drop under the recommended 3% (3.6V), you must upsize to 10 AWG copper, which brings the drop down to roughly 2.4%. Always use a dedicated voltage drop calculator for runs exceeding 75 to 100 feet.
