For standard residential branch circuits using copper wire, the most queried values on any wire size chart AWG are: 14 AWG (15 Amps), 12 AWG (20 Amps), 10 AWG (30 Amps), 8 AWG (40 Amps), and 6 AWG (55 Amps for NM-B / 65 Amps for THHN). These baseline numbers assume a standard 30°C (86°F) ambient temperature, no more than three current-carrying conductors in a raceway, and standard residential termination equipment.
While memorizing the top five sizes gets you through most weekend projects, pulling the correct wire for subpanels, HVAC disconnects, or long feeder runs requires a precise reading of the National Electrical Code (NEC) ampacity tables. Below is the exact data you need, structured for quick jobsite lookups.
How to Read the NEC Wire Size Chart AWG
The definitive source for wire ampacities in the United States is NEC Table 310.16 (formerly Table 310.15(B)(16) prior to the 2020 code cycle). This table dictates the allowable ampacities for insulated conductors rated up to 2000 volts.
How to read this table: The rows represent the American Wire Gauge (AWG) or kcmil size. The columns represent the temperature rating of the wire's insulation (60°C, 75°C, and 90°C). To use the table correctly, you must first identify the insulation type printed on the wire jacket (e.g., THHN is 90°C, NM-B is 60°C) and then apply the termination rules outlined in NEC 110.14(C) to determine which column actually governs your final breaker size.
Bookmark these quick-jump rows for the most common residential copper sizes:
- 14 AWG: 15A (60°C) | 20A (75°C) | 25A (90°C)
- 12 AWG: 20A (60°C) | 25A (75°C) | 30A (90°C)
- 10 AWG: 30A (60°C) | 35A (75°C) | 40A (90°C)
- 8 AWG: 40A (60°C) | 50A (75°C) | 55A (90°C)
- 6 AWG: 55A (60°C) | 65A (75°C) | 75A (90°C)
| AWG / kcmil Size | 60°C (140°F) Column | 75°C (167°F) Column | 90°C (194°F) Column | Common Insulation Types |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A | TW, UF |
| 12 AWG | 20 A | 25 A | 30 A | TW, UF, THHN |
| 10 AWG | 30 A | 35 A | 40 A | TW, UF, THHN |
| 8 AWG | 40 A | 50 A | 55 A | THW, THHN, XHHW |
| 6 AWG | 55 A | 65 A | 75 A | THW, THHN, XHHW |
| 4 AWG | 70 A | 85 A | 95 A | THW, THHN, XHHW |
| 3 AWG | 85 A | 100 A | 110 A | THW, THHN, XHHW |
| 2 AWG | 95 A | 115 A | 130 A | THW, THHN, XHHW |
| 1 AWG | 110 A | 130 A | 145 A | THW, THHN, XHHW |
| 1/0 AWG | 125 A | 150 A | 170 A | THW, THHN, XHHW |
| 2/0 AWG | 145 A | 175 A | 195 A | THW, THHN, XHHW |
Note: These values apply to copper conductors. For aluminum, consult the right side of NEC Table 310.16, which yields significantly lower ampacities for the same gauge. For a manufacturer-verified lookup, refer to the Southwire Ampacity Chart.
Which Temperature Column Applies to Your Installation
The most common mistake DIYers and junior apprentices make is looking at a spool of THHN wire, seeing '90°C' printed on the jacket, and immediately sizing their breaker using the 90°C column. This is a code violation and a fire hazard. Here is how to determine which column actually governs your circuit.
When to use the 60°C Column
You must use the 60°C column if you are using NM-B (Romex) or UF-B cable. Per NEC 334.80, the ampacity of NM-B cable is strictly limited to the 60°C column, regardless of the fact that the internal conductors might technically have 90°C insulation. You also use this column if you are terminating into older equipment or devices explicitly marked '60°C Only'.
When to use the 75°C Column
You use the 75°C column when pulling individual THHN/THWN-2 or XHHW conductors through conduit to standard 75°C-rated breakers, panel lugs, or heavy-duty receptacles (like a 50A range receptacle). This is the standard column for sizing branch circuits over 50A and most residential subpanel feeders.
When to use the 90°C Column
The 90°C column is almost never used to determine your final breaker size in residential work. Its primary legal purpose is to serve as the starting baseline for derating calculations (explained below). It can also be used for equipment termination points specifically listed and rated for 90°C, which are rare in standard residential panels but common in industrial control cabinets.
Derating and What the Chart Cannot Tell You
A wire size chart AWG reference is a baseline, not a final answer. The numbers in Table 310.16 assume perfect conditions: an ambient temperature of exactly 30°C (86°F) and no more than three current-carrying conductors bundled together. When real-world conditions deviate, you must apply adjustment factors.
How Derating Modifies the Base Value
When you pull more than three current-carrying conductors through a single conduit, the heat generated by the wires cannot dissipate properly. NEC Table 310.15(C)(1) mandates that you multiply the wire's base ampacity by a derating percentage.
Worked Example: You are running a 240V circuit plus a neutral for a multi-wire setup, resulting in four current-carrying 12 AWG THHN conductors in one PVC conduit.
1. Base ampacity for 12 AWG THHN (90°C column) = 30A.
2. Adjustment factor for 4-6 conductors (per NEC 310.15(C)(1)) = 80%.
3. Derated ampacity = 30A × 0.80 = 24 Amps.
Because 24A is still greater than the 20A breaker you plan to use (and the 75°C termination limit of 25A), 12 AWG THHN remains code-compliant for this run. If you had 10 current-carrying conductors (50% derating), 30A × 0.50 = 15A, meaning 12 AWG would fail and you would need to step up to 10 AWG.
What the Table Cannot Tell You
Relying solely on an ampacity chart leaves three critical engineering factors unaddressed. If you ignore these, your installation may be 'code compliant' on paper but fail in practice.
- Voltage Drop: NEC Table 310.16 does not account for distance. If you run 14 AWG copper 120 feet to a 12A window AC unit, the wire won't melt (it's under the 15A limit), but the voltage drop will exceed the NEC-recommended 3% threshold for branch circuits. The compressor will struggle to start, draw locked-rotor current, and eventually burn out. For runs over 50 feet, always calculate voltage drop using the formula: VD = (2 × K × I × D) / CM (where K is 12.9 for copper, I is current, D is one-way distance, and CM is circular mils from NEC Chapter 9, Table 8).
- Physical Lug Fit and Torque: The chart tells you 6 AWG is rated for 65A at 75°C, but it doesn't tell you that a standard 20A duplex receptacle's screw terminals physically cannot accommodate 6 AWG wire. Furthermore, per NEC 110.14(D), you must tighten terminations to the manufacturer's specified torque using a calibrated torque screwdriver or wrench. Over-torquing a small lug with large wire can strip the threads or snap the screw; under-torquing causes high-resistance connections that arc and start fires.
- Short-Circuit Withstand Rating: Ampacity charts measure continuous thermal limits, not fault conditions. If a 100A fault occurs on a circuit protected by a 100A breaker with a high let-through current, a smaller gauge wire might vaporize before the breaker's magnetic trip clears the fault. This is why equipment grounding conductors (EGCs) must be sized per NEC Table 250.122 based on the breaker size, not just the circuit load.
For the most current code updates and official interpretations on conductor sizing, always consult the National Fire Protection Association (NFPA) NEC portal. Remember that local Authorities Having Jurisdiction (AHJ) may adopt amendments that supersede general NEC guidance, so always verify with your local inspector before pulling wire for large feeders.
