How to Read This Wire Amperage Capacity Chart
Before you strip a single wire, you need to understand the three variables that dictate ampacity: material (copper vs. aluminum), insulation temperature rating (60°C, 75°C, or 90°C), and the termination temperature rating of your equipment. The most common mistake DIYers and junior electricians make is looking exclusively at the 90°C column because it offers the highest numbers. Unless your lugs, breakers, and devices are explicitly rated for 90°C (which is exceptionally rare in residential and light commercial work), you cannot use that column for your final breaker sizing.
The Master Wire Amperage Capacity Chart (NEC Table 310.16)
The following data is extracted directly from NEC Table 310.16 (2020/2023 editions), the definitive standard for conductor ampacities in raceways or cables with an ambient temperature of 30°C (86°F). Bookmark this section for quick jobsite lookups.
| AWG / kcmil | Copper 60°C (140°F) | Copper 75°C (167°F) | Copper 90°C (194°F) | Aluminum 60°C | Aluminum 75°C | Aluminum 90°C |
|---|---|---|---|---|---|---|
| 14 | 15A * | 20A * | 25A * | - | - | - |
| 12 | 20A * | 25A * | 30A * | - | - | - |
| 10 | 30A * | 35A * | 40A * | - | - | - |
| 8 | 40A | 50A | 55A | 30A | 40A | 45A |
| 6 | 55A | 65A | 75A | 40A | 50A | 55A |
| 4 | 70A | 85A | 95A | 55A | 65A | 75A |
| 3 | 85A | 100A | 110A | 65A | 75A | 85A |
| 2 | 95A | 115A | 130A | 75A | 90A | 100A |
| 1 | 110A | 130A | 145A | 85A | 100A | 115A |
| 1/0 | 125A | 150A | 170A | 100A | 120A | 135A |
| 2/0 | 145A | 175A | 195A | 115A | 135A | 150A |
| 3/0 | 165A | 200A | 225A | 130A | 155A | 175A |
| 4/0 | 195A | 230A | 260A | 150A | 180A | 205A |
* Note: While the 75°C and 90°C columns show higher values for 14, 12, and 10 AWG, NEC 240.4(D) strictly limits the overcurrent protection (breaker size) for these small conductors to 15A, 20A, and 30A respectively, unless specific motor/compressor exceptions apply.
For deeper code context, refer to the NFPA 70 National Electrical Code documentation or training resources from Mike Holt Enterprises.
Derating: When the Base Ampacity Drops
The chart above assumes two ideal conditions: an ambient temperature of exactly 86°F (30°C) and no more than three current-carrying conductors bundled in a single raceway. When you violate either assumption, the base ampacity drops. This is where installations fail and wires melt inside walls.
1. Ambient Temperature Derating: If you are running THHN through an attic in Arizona where ambient temperatures hit 120°F (49°C), you must apply a temperature correction factor. For 90°C THHN at 120°F, the correction factor is 0.82. A 6 AWG copper wire (90°C column = 75A) drops to 61.5A (75 x 0.82).
2. Bundling Derating (More than 3 conductors): If you pull four current-carrying conductors (e.g., two hot wires for a multi-wire branch circuit, plus two hots for another circuit, sharing a neutral) through a single conduit, you must apply an 80% adjustment factor.
Decision Path: Pick Your Exact Wire and Breaker
Stop guessing. Use this decision tree to select the exact wire gauge and breaker size for standard residential copper branch circuits and feeders. This assumes standard 75°C rated terminations and NM-B (Romex) or THHN in conduit.
| If Your Load / Breaker is... | Use this Wire (NM-B Cable) | Use this Wire (THHN in Conduit) | Why This is the Concrete Pick |
|---|---|---|---|
| 15 Amps | 14 AWG Cu | 14 AWG Cu | 14 AWG is legally capped at 15A per NEC 240.4(D). |
| 20 Amps | 12 AWG Cu | 12 AWG Cu | 12 AWG is legally capped at 20A. Standard for kitchen/bath receptacles. |
| 30 Amps | 10 AWG Cu | 10 AWG Cu | 10 AWG is capped at 30A. Used for standard dryers and RV outlets. |
| 40 Amps | 8 AWG Cu | 8 AWG Cu | 8 AWG NM-B is rated 40A (60°C col). 8 AWG THHN is 50A (75°C col). |
| 50 Amps | 6 AWG Cu | 8 AWG Cu | NM-B is limited to 60°C col (6 AWG = 55A, so 6 AWG is required). THHN uses 75°C col (8 AWG = 50A). |
| 60 Amps | 4 AWG Cu | 6 AWG Cu | Critical trap: 6 AWG NM-B is only 55A and CANNOT be used on a 60A breaker. Use 4 AWG NM-B or 6 AWG THHN. |
| 100 Amps (Subpanel) | 3 AWG Cu / 1 AWG Al | 3 AWG Cu / 1 AWG Al | Sized via 75°C column. Aluminum is the cost-effective standard for feeders. |
| 200 Amps (Service) | N/A (Use SER) | 2/0 Cu / 4/0 Al | Standard residential service entrance sizing based on 310.12. |
What This Chart Cannot Tell You
While NEC Table 310.16 is the bible for thermal limits, it is completely blind to three critical jobsite realities. If you ignore these, your installation might not melt, but it will fail to function properly or pass inspection.
- Voltage Drop Over Distance: Ampacity only tells you what the wire can handle before the insulation melts. It does not guarantee the voltage at the end of the run is usable. For runs exceeding 100 feet, you must calculate voltage drop using the circular mil area from NEC Chapter 9, Table 8. A 6 AWG wire on a 50A load might be thermally safe, but 150 feet away, your 240V well pump might only see 215V, causing the motor to overheat and trip its internal overload. Aim for a maximum 3% drop on branch circuits and 5% total drop from service to appliance.
- Conduit Fill Capacity: The chart assumes you can physically fit the wires in the raceway. If you try to pull four 4/0 AWG aluminum conductors into a 1-inch PVC conduit, you will exceed the 40% fill capacity mandated by NEC Chapter 9, Table 1. You will need to step up to 1.5-inch or 2-inch conduit to avoid jamming and damaging the insulation during the pull.
- Equipment Grounding Conductor (EGC) Sizing: The ampacity chart applies to current-carrying conductors. For the ground wire, you must use NEC Table 250.122. On a 400A feeder using 600 kcmil copper, your hots are massive, but your EGC only needs to be 3 AWG copper. Sizing the ground wire using 310.16 is a waste of copper and money.
- Short-Circuit Interrupting Capacity (AIC): This chart has nothing to do with fault currents. If your utility transformer can deliver 22,000 amps of fault current, your breaker must have a 22k AIC rating, regardless of the wire size connected to it.
