For standard residential branch circuits, the baseline rule of thumb is simple: 14 AWG is rated for 15 amps, 12 AWG for 20 amps, and 10 AWG for 30 amps. However, the exact allowable ampacity depends entirely on the wire's insulation temperature rating and the terminal temperature limits of your connected devices, as governed by the National Electrical Code (NEC). If you are sizing feeders, subpanels, or heavy appliance circuits, guessing from memory will result in either a failed inspection or a melted terminal lug. This guide breaks down the official amp chart for wire sizing, explains how to apply derating factors, and answers the most common long-tail sizing questions.
How to Read This Wire Amp Chart
Before looking at the numbers, you must understand the assumptions baked into the NEC ampacity tables. The chart below is derived directly from NEC Table 310.16 (formerly 310.15(B)(16)) and assumes an ambient temperature of 30°C (86°F) with no more than three current-carrying conductors in a raceway.
Which column applies to your installation? This is where most DIYers and junior apprentices make critical errors. Under NEC 110.14(C), you must use the temperature column that matches the lowest rated component in the circuit.
- 60°C Column: Mandatory for circuits rated 100A or less, unless the equipment is specifically marked for 75°C. Standard NM-B (Romex) cable is strictly limited to the 60°C column regardless of the 90°C rating of the individual THHN conductors inside it.
- 75°C Column: Used for circuits over 100A, or for 100A-and-under circuits where both the wire (e.g., THHN/THWN-2) and the equipment terminals (like modern panel lugs and large breakers) are explicitly rated for 75°C.
- 90°C Column: Almost never used for final ampacity in residential work. It is primarily used as a starting point for calculating derating adjustments before comparing the result back to the 60°C or 75°C column.
The Complete NEC Table 310.16 Ampacity Chart
Below is the complete data table for common residential and light-commercial wire sizes. Source standard: NFPA 70 (National Electrical Code), Table 310.16.
| AWG / kcmil | Cu 60°C | Cu 75°C | Cu 90°C | Al 60°C | Al 75°C | Al 90°C |
|---|---|---|---|---|---|---|
| 14 | 15 | 20 | 25 | — | — | — |
| 12 | 20 | 25 | 30 | 15 | 20 | 25 |
| 10 | 30 | 35 | 40 | 25 | 30 | 35 |
| 8 | 40 | 50 | 55 | 30 | 40 | 45 |
| 6 | 55 | 65 | 75 | 40 | 50 | 60 |
| 4 | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 | 195 | 230 | 260 | 150 | 180 | 205 |
• 12 AWG Copper: 20A (60°C column) — Standard 20A receptacle circuits using NM-B.
• 6 AWG Copper: 55A (60°C) / 65A (75°C) — Used for 50A and 60A subpanel feeders and EV chargers.
• 2 AWG Aluminum: 90A (75°C) — The standard, cost-effective choice for 100A subpanel feeders (requires 75°C rated lugs).
Derating Factors and What the Chart Cannot Tell You
The base ampacities above assume ideal conditions. In the real world, you must apply derating factors that modify the base value before selecting your breaker.
How Derating Modifies the Base Value: Under NEC Table 310.15(C)(1), if you pull more than three current-carrying conductors in a single conduit, the wires heat each other up. For 4 to 6 conductors, you must multiply the base ampacity by 80%. For 7 to 9 conductors, you multiply by 70%. Furthermore, if your attic or rooftop conduit exceeds 30°C (86°F), you must apply ambient temperature correction factors from NEC Table 310.15(B)(1). You always start your derating math using the 90°C column, but the final derated number cannot exceed the standard 60°C or 75°C ampacity limit.
What the Table Cannot Tell You: An amp chart for wire sizing only addresses thermal limits under continuous load. It does not account for:
- Voltage Drop: NEC 310.15(B) is an informational note, but best practice (and strict code in some local jurisdictions) demands keeping voltage drop under 3% for branch circuits and 5% total. A long 100-foot run of 10 AWG to a 30A RV outlet might be thermally safe, but the voltage drop will starve the RV's AC compressor. You must upsized for distance.
- Conduit Fill: Chapter 9 of the NEC limits how much physical space wires can take up in a pipe (usually 40% for three or more wires). You might need a larger conduit even if the ampacity is fine.
- Short-Circuit Withstand: The chart assumes the breaker trips in time to save the wire. If your available fault current is massive (e.g., near a utility transformer), the let-through current might melt a smaller wire before the magnetic trip engages.
Wire Amp Chart FAQ
What size wire do I need for a 50 amp breaker?
For a 50-amp circuit, you need 6 AWG copper if your terminals are rated for 75°C (which most modern 50A breakers and range receptacles are). If you are using older equipment or NM-B cable where terminals are strictly limited to 60°C, you must upgrade to 4 AWG copper. For aluminum, you need 4 AWG at 75°C. Always check the manufacturer's spec sheet for the specific breaker and receptacle to confirm the terminal temperature rating.
Can I use the 90°C column to downsize my wire for residential breakers?
No. While THHN and XHHW-2 wire insulation is rated for 90°C, standard residential breakers and panel lugs (up to 100A) are generally only rated for 60°C or 75°C. NEC 110.14(C) dictates that the final circuit ampacity cannot exceed the rating of the lowest-rated component. You can use the 90°C column to calculate derating adjustments for bundling or high ambient heat, but the final adjusted ampacity must still fall within the limits of the 60°C or 75°C column.
Does this amp chart wire data apply to 12V or 24V DC solar systems?
Technically, the thermal ampacity limits in NEC Table 310.16 apply to both AC and DC current. However, in low-voltage DC solar systems, voltage drop is the governing constraint, not thermal ampacity. A 10 AWG wire might safely carry 30A thermally, but pushing 30A at 12V through 20 feet of 10 AWG wire results in a nearly 10% voltage drop, which will severely impact solar charge controller efficiency and battery charging profiles. For DC solar sizing, always calculate voltage drop first, then verify the resulting wire size against the NEC thermal amp chart.
Why is my 10 AWG wire melting on a 30 amp circuit if the chart says it is safe?
If your wire is melting or the insulation is scorching at the termination point, the issue is almost certainly a high-resistance connection, not an undersized wire. Loose terminal screws create arcing and localized heat that far exceeds the wire's thermal rating. This is why NEC 110.14(D) now requires the use of a calibrated torque screwdriver or wrench to tighten terminals to the manufacturer's specified inch-pound settings. A 10 AWG wire on a 30A double-pole breaker should typically be torqued to around 45-50 in-lbs, but always verify the exact value printed on the breaker's label.
