For standard residential branch circuits, 14 AWG copper wire handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. An AWG (American Wire Gauge) sizes chart maps a wire's cross-sectional area to its maximum safe current-carrying capacity, known as ampacity. However, simply matching a wire gauge to a breaker size based on a single number is a common trap that leads to overheated terminations and failed inspections.
How to read this chart: The master table below is based on NEC Table 310.16 for copper conductors. It is divided into three temperature columns: 60°C, 75°C, and 90°C. These columns represent the thermal rating of the wire's insulation (e.g., NM-B is typically 60°C/90°C, while THHN is 90°C). The final column lists the standard maximum overcurrent protection (breaker size) permitted under NEC 240.4(D) for small conductors. Keep this page bookmarked for quick-jump reference on the bench or in the panel.
• 14 AWG: 15A max breaker (Lighting/receptacles)
• 12 AWG: 20A max breaker (Kitchen/bathroom receptacles)
• 10 AWG: 30A max breaker (Dryers/water heaters)
• 6 AWG: 60A max breaker (Subpanels/EV chargers)
• 4 AWG: 80A max breaker (Large subpanels)
The Master AWG Sizes Chart (NEC Table 310.16)
The following data applies to copper conductors with an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable.
| AWG Size | 60°C (140°F) Ampacity | 75°C (167°F) Ampacity | 90°C (194°F) Ampacity | Standard Max Breaker (NEC 240.4) |
|---|---|---|---|---|
| 14 | 15A | 20A | 25A | 15A |
| 12 | 20A | 25A | 30A | 20A |
| 10 | 30A | 35A | 40A | 30A |
| 8 | 40A | 50A | 55A | 40A |
| 6 | 55A | 65A | 75A | 60A |
| 4 | 70A | 85A | 95A | 80A |
| 3 | 85A | 100A | 115A | 100A |
| 2 | 95A | 115A | 130A | 115A / 125A |
| 1 | 110A | 130A | 145A | 130A / 150A |
| 1/0 | 125A | 150A | 170A | 150A |
| 2/0 | 145A | 175A | 195A | 175A |
| 3/0 | 165A | 200A | 225A | 200A |
| 4/0 | 195A | 230A | 260A | 225A / 250A |
Source: NFPA 70 National Electrical Code (NEC), Table 310.16. For official code compliance, always consult the latest adopted edition in your jurisdiction via the NFPA NEC portal.
Which Ampacity Column Applies to Your Installation?
The most frequent mistake DIYers and junior apprentices make is looking at a spool of 90°C-rated THHN wire, seeing '40A' in the 90°C column for 8 AWG, and slapping it on a 40A breaker for a circuit with standard residential devices. This violates NEC 110.14(C) and creates a fire hazard at the termination points.
Here is the exact decision framework for selecting your column:
- The 60°C Column (The Default): NEC 110.14(C)(1)(a) mandates that for circuits rated 100A or less, or for conductors sized 14 AWG through 1 AWG, you must use the 60°C column to determine final ampacity. This is because standard residential breakers, receptacles, and switches are typically only tested and rated for 60°C terminations. Even if your wire is THHN (90°C), the weakest link (the terminal) dictates the rule.
- The 75°C Column (The Exception): You may use the 75°C column only if the equipment terminations (both the breaker lugs and the device lugs) are explicitly marked and rated for 75°C. This is common in larger commercial panels, subpanel lugs, and heavy-duty equipment disconnects. For example, 4 AWG copper at 75°C yields 85A, allowing you to use the next standard size up (90A breaker) under NEC 240.4(B).
- The 90°C Column (The Derating Starting Point): You almost never use the 90°C column for your final base ampacity at the termination. Its primary purpose is to serve as the starting baseline for derating calculations when you have multiple wires in a conduit or high ambient temperatures.
How Derating and Bundling Modify Base Ampacity
When you pull more than three current-carrying conductors through a single raceway (conduit), the wires heat each other up. The base ampacity in the chart above assumes only three current-carrying conductors. To find your true safe ampacity, you must apply the adjustment factors from NEC Table 310.15(C)(1).
Imagine you are pulling four 12 AWG THHN wires (two hots, one neutral, one ground) through a single EMT conduit to feed a multi-wire branch circuit.
1. Identify current-carrying conductors: The ground does not count. You have 3 current-carrying conductors. No derating required yet.
2. Add a second circuit: Now you pull 8 wires (4 hots, 2 neutrals, 2 grounds). You now have 6 current-carrying conductors.
3. Find the multiplier: NEC Table 310.15(C)(1) dictates an 80% adjustment factor for 4 to 6 conductors.
4. Calculate: Start with the 90°C column for 12 AWG THHN (30A). Multiply 30A × 0.80 = 24A.
5. Verify termination limit: Your derated ampacity (24A) is higher than the 60°C termination limit for 12 AWG (20A). Therefore, you can still safely use a 20A breaker.
Warning: If you added a third circuit (9 current-carrying conductors), the derating factor drops to 70%. 30A × 0.70 = 21A. Still acceptable for a 20A breaker. But at 10 conductors (50% factor), 30A × 0.50 = 15A. You must now drop to a 15A breaker or upsize to 10 AWG wire.
Always remember that the final derated ampacity must still be equal to or greater than the termination limit dictated by the 60°C or 75°C column. You cannot use a 90°C derated value to terminate on a 60°C rated lug.
What This AWG Chart Cannot Tell You (Voltage Drop & Edge Cases)
An ampacity chart guarantees the wire will not melt or catch fire under a specific load. It does not guarantee the equipment at the end of the wire will function correctly. Relying solely on Table 310.16 without considering the following variables is how you end up with dim lights, tripping motors, and fried electronics.
1. Voltage Drop Over Distance
The chart assumes relatively short runs. When wire runs exceed 50 to 100 feet, the inherent resistance of copper causes voltage to drop. While the NEC treats voltage drop as an informational note (NEC 310.15(B)) rather than a strict enforceable mandate for most residential branch circuits, best practice and equipment manufacturers demand a maximum 3% drop on branch circuits and 5% total drop from the service entrance.
For example, pulling 40 amps through 6 AWG copper over a 150-foot run to a detached garage subpanel will result in a voltage drop exceeding 4%. To maintain a tight 3% drop at 240V, you must upsize to 4 AWG or even 3 AWG copper, despite the ampacity chart saying 6 AWG is sufficient for the thermal load. Use the Copper Development Association voltage drop calculator for exact math on long feeder runs.
2. Ambient Temperature Corrections
The base chart assumes an ambient temperature of 30°C (86°F). If you are routing NM-B cable through an attic in the middle of summer where temperatures routinely hit 50°C (122°F), or running THHN through a conduit on a sun-baked exterior wall, the wire's ability to shed heat is compromised. You must apply the temperature correction factors from NEC Table 310.15(B)(1). At 50°C ambient, a 90°C rated wire must be derated to 82% of its base ampacity.
3. Aluminum vs. Copper
This chart is strictly for copper. Aluminum conductors have higher resistance and require larger gauges to carry the same current. For instance, while 3 AWG copper is standard for a 100A subpanel feeder (using the 75°C column), you must step up to 1/0 AWG aluminum for the exact same 100A load. Never use a copper chart to size aluminum wire, and always ensure your lugs are rated for aluminum (often marked AL/CU) and treated with an anti-oxidant compound like Noalox.
