The maximum AWG wire amperage depends on the insulation temperature rating and the terminal rating of the connected equipment. For standard residential branch circuits (15A to 50A), you generally use the 60°C column for 14, 12, and 10 AWG, and the 75°C column for 8 AWG and larger, per NEC 110.14(C). This guide provides the complete lookup table, derating mathematics, and the edge cases that cause failed inspections.
How to Read the AWG Wire Amperage Table
The table below is sourced directly from NFPA 70: National Electrical Code (NEC) Table 310.16. It lists the allowable ampacities for insulated copper conductors rated up to 2000 volts. Before you pick a wire size, you must understand the three temperature columns and the 'weakest link' rule.
Which column applies to your installation?
- 60°C Column (TW, UF): Mandatory for 14, 12, and 10 AWG conductors on circuits rated 100A or less, unless the equipment is explicitly marked otherwise. Also used for NM-B (Romex) cable, which is internally limited to 60°C regardless of the wire's individual insulation.
- 75°C Column (RHW, THHW, THW, THWN, XHHW): The standard for most commercial and residential feeders, subpanels, and branch circuits 8 AWG and larger connected to 75°C rated lugs.
- 90°C Column (THHN, THWN-2, XHHW-2): Used almost exclusively as the starting point for derating calculations (ambient temperature and conduit bundling). The final derated value is then compared against the 75°C terminal limit, and the lower of the two numbers wins.
The Complete AWG Wire Amperage Chart (Copper)
Below is the complete reference chart for copper conductors in a standard 30°C (86°F) ambient environment.
14 AWG = 20A (Limited to 15A by NEC 240.4(D))
12 AWG = 25A (Limited to 20A by NEC 240.4(D))
10 AWG = 35A (Limited to 30A by NEC 240.4(D))
8 AWG = 50A | 6 AWG = 65A | 4 AWG = 85A | 2 AWG = 115A | 1/0 AWG = 150A | 4/0 AWG = 230A
| AWG Size | 60°C (140°F) TW, UF |
75°C (167°F) RHW, THHW, THW, THWN |
90°C (194°F) THHN, THHW, THW-2, THWN-2 |
|---|---|---|---|
| 14 | 15 | 20 | 25 |
| 12 | 20 | 25 | 30 |
| 10 | 30 | 35 | 40 |
| 8 | 40 | 50 | 55 |
| 6 | 55 | 65 | 75 |
| 4 | 70 | 85 | 95 |
| 3 | 85 | 100 | 110 |
| 2 | 95 | 115 | 130 |
| 1 | 110 | 130 | 145 |
| 1/0 | 125 | 150 | 170 |
| 2/0 | 145 | 175 | 195 |
| 3/0 | 165 | 200 | 225 |
| 4/0 | 195 | 230 | 260 |
Source: NEC Table 310.16. Values assume not more than three current-carrying conductors in a raceway or cable, and an ambient temperature of 30°C (86°F).
What the Chart Cannot Tell You (Derating & Limits)
A common mistake on the jobsite is treating the table above as the final word. The chart assumes ideal conditions. In the real world, you must account for environmental factors and physical limitations.
How Derating Rows Modify the Base Value
When you pull more than three current-carrying conductors through a single conduit, or when the ambient temperature exceeds 86°F (30°C), the wires cannot dissipate heat effectively. You must apply correction and adjustment factors.
Numeric Example: You are pulling four 4/0 AWG THHN (90°C) current-carrying conductors through a conduit in a boiler room where the ambient temperature is 104°F (40°C).
- Base Ampacity: The 90°C column for 4/0 AWG is 260A.
- Temperature Correction: Per NEC Table 310.15(B)(1), the correction factor for 90°C wire at 104°F is 0.91. (260A × 0.91 = 236.6A).
- Bundling Adjustment: Per NEC Table 310.15(C)(1), 4 to 6 current-carrying conductors require an 80% adjustment factor. (236.6A × 0.80 = 189.28A).
- Terminal Limit Check: Your panel lugs are rated 75°C. The 75°C column for 4/0 AWG is 230A. Since your derated value (189.28A) is lower than the terminal limit (230A), your final allowable ampacity is 189.28A.
Per NEC 240.4(B), because 189.28A does not correspond to a standard breaker size, you are permitted to round up to the next standard size, which is a 200A breaker.
What This Table Cannot Tell You
- Voltage Drop: NEC 310.16 only addresses thermal limits (fire safety). It does not guarantee your equipment will run properly. A 6 AWG wire on a 60A breaker is thermally safe at 65 feet, but at 150 feet, the voltage drop will exceed the recommended 3% limit for branch circuits. You must calculate voltage drop separately for long runs.
- Physical Lug Fit: The chart tells you that 1/0 AWG is good for 150A. However, many standard 100A and 125A residential main breaker lugs are not physically large enough to accept 1/0 AWG wire. Always check the manufacturer's datasheet for the breaker's maximum wire gauge acceptance before purchasing.
- Short-Circuit Withstand: Ampacity is about continuous thermal loading. Under a massive short-circuit fault, the magnetic trip of the breaker handles the event, but the wire must withstand the thermal stress for the milliseconds before the breaker clears. This is governed by NEC 110.10 and equipment let-through current ratings, not Table 310.16.
For deeper calculations on conduit fill and thermal limits, refer to resources like Electrical Contractor Magazine's code analysis section.
AWG Wire Amperage FAQ
What is the max amperage for 12 AWG wire?
Thermally, 12 AWG copper is rated for 20A at 60°C, 25A at 75°C, and 30A at 90°C. However, NEC 240.4(D) specifically restricts small conductors to prevent overheating in standard residential applications. Regardless of the insulation type, the maximum overcurrent protection (breaker size) for 12 AWG copper is strictly limited to 20 amps.
Can I use the 90°C column for THHN wire ampacity?
You can only use the 90°C column as the starting point for derating calculations (like the conduit bundling example above). You cannot use the 90°C value as your final circuit ampacity unless every single termination point in the circuit (breaker, receptacle, splice block) is explicitly rated for 90°C, which is exceptionally rare in standard commercial and residential gear.
Does AWG wire amperage change for aluminum wire?
Yes, significantly. Aluminum has higher electrical resistance and lower thermal conductivity than copper, meaning it generates more heat and dissipates it slower. For example, while 2 AWG copper is rated for 115A in the 75°C column, 2 AWG aluminum (like XHHW-2 or THWN-2) is only rated for 90A in the 75°C column. Always ensure you are looking at the copper table, not the aluminum table, when using the chart above.
How does bundling wires in conduit affect AWG amperage?
When wires are bundled together in a conduit, the heat generated by one wire warms the adjacent wires. If you have 4 to 6 current-carrying conductors in a single raceway, you must multiply the wire's base ampacity by 0.80 (an 80% derating). For 7 to 9 conductors, the factor drops to 0.70 (70%). Note that equipment grounding conductors (EGCs) do not count as current-carrying conductors for this calculation, but neutral conductors carrying unbalanced current on a 3-phase wye system or nonlinear loads do count.
Why is NM-B (Romex) limited to the 60°C column even if the wires inside are 90°C?
NM-B cable contains individual conductors that are typically THHN (90°C rated). However, the outer PVC jacket of the cable assembly traps heat and has a lower melting point. Therefore, NEC 334.80 mandates that the ampacity of NM-B cable must be determined using the 60°C column, regardless of the internal wire's higher temperature rating. A 6 AWG NM-B cable is therefore limited to 55A, not the 75A it would achieve if pulled as individual THHN wires in a conduit.
