For standard residential and light commercial branch circuits, the most queried wire chart amps values are 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A). These baseline numbers come directly from the 60°C column of NEC Table 310.16. However, pulling a single number from a chart without understanding the temperature columns, termination limits, and derating factors is the fastest way to fail an inspection or, worse, start a fire inside a conduit.
This reference guide provides the complete copper ampacity table, explains exactly which column applies to your specific installation, and breaks down the derating math that modifies these base values in real-world jobsite conditions.
How to Read the NEC Wire Chart Amps Table
The ampacity of a conductor is not a single fixed number; it changes based on the thermal limits of the insulation and the equipment it connects to. When looking at the NFPA 70: National Electrical Code (NEC) Table 310.16, you will see three primary temperature columns for copper: 60°C (140°F), 75°C (167°F), and 90°C (194°F).
Bookmark-Friendly Quick Jumps
For standard 120V/240V residential branch circuits (using the conservative 60°C column), here are the baseline maximum overcurrent protection limits:
- 14 AWG: 15 Amps (Lighting and general receptacles)
- 12 AWG: 20 Amps (Kitchen/bathroom receptacles, window ACs)
- 10 AWG: 30 Amps (Electric dryers, RV outlets, water heaters)
- 8 AWG: 40 Amps (EV Level 2 chargers, large cooktops)
- 6 AWG: 55 Amps (Often used for 60A subpanels, though 60A breakers require specific 75°C termination checks)
Complete Copper Wire Chart Amps (NEC Table 310.16)
The table below lists the allowable ampacities for insulated copper conductors rated up to 2000 volts. These values assume an ambient air temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable.
| Size (AWG/kcmil) | 60°C (140°F) TW, UF |
75°C (167°F) THHW, THWN |
90°C (194°F) THHN, XHHW |
|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A |
| 12 AWG | 20 A | 25 A | 30 A |
| 10 AWG | 30 A | 35 A | 40 A |
| 8 AWG | 40 A | 50 A | 55 A |
| 6 AWG | 55 A | 65 A | 75 A |
| 4 AWG | 70 A | 85 A | 95 A |
| 3 AWG | 85 A | 100 A | 110 A |
| 2 AWG | 95 A | 115 A | 130 A |
| 1 AWG | 110 A | 130 A | 145 A |
| 1/0 AWG | 125 A | 150 A | 170 A |
| 2/0 AWG | 145 A | 175 A | 195 A |
| 3/0 AWG | 165 A | 200 A | 225 A |
| 4/0 AWG | 195 A | 230 A | 260 A |
Derating and What the Wire Chart Amps Table Cannot Tell You
The base numbers in Table 310.16 are best-case scenarios. On a real jobsite, you must apply derating factors that reduce the allowable ampacity. If the derated ampacity drops below your breaker size, you must increase the wire gauge.
How Derating Modifies the Base Value
There are two primary derating triggers that multiply against your base wire chart amps:
- Ambient Temperature: If your conduit runs through a hot attic or above a roof, the 30°C (86°F) baseline is exceeded. For example, an attic at 114°F (46°C) requires a correction factor of 0.82 for THHN (90°C) wire.
- Conductor Bundling: When you pull more than three current-carrying conductors through a single conduit, they heat each other up. Four to six conductors require an 80% adjustment factor (0.80); seven to nine require 70% (0.70).
Worked Example: You are pulling two 240V circuits (4 current-carrying hot wires total, neutrals do not count on a standard 240V straight resistive load) through an attic conduit that hits 114°F. You want to use 12 AWG THHN.
Base 90°C ampacity: 30A.
Temperature correction (114°F): 30A × 0.82 = 24.6A.
Bundling adjustment (4 conductors): 24.6A × 0.80 = 19.68A.
Result: 19.68A is less than the 20A breaker you planned to use. You must upsize to 10 AWG THHN to maintain a safe 20A circuit under these conditions. (For a deeper dive into the physics of conductor heating, see All About Circuits: Wire Sizing).
What the Table Cannot Tell You
Relying solely on ampacity charts leaves three critical blind spots in your design:
- Voltage Drop: Table 310.16 does not account for distance. A 12 AWG wire is legally rated for 20A at 10 feet or 100 feet. However, at 100 feet on a 20A load, you will experience roughly a 6.4% voltage drop on a 120V circuit. The NEC recommends keeping branch circuit voltage drop under 3%. For long runs, you must size up for voltage drop, not just ampacity.
- Conduit Fill Capacity: The chart tells you how much current a wire can carry, but NEC Chapter 9 dictates how many wires physically fit inside a conduit. You cannot jam six 6 AWG THHN wires into a 1/2-inch EMT conduit, regardless of derating math.
- Local AHJ Amendments: Your local Authority Having Jurisdiction (inspector) may have regional amendments that supersede the national code, such as mandating copper-only feeders or banning specific insulation types in plenums.
Wire Chart Amps FAQ
Can I use the 90°C column for residential wire chart amps sizing?
You can only use the 90°C column for derating calculations (like the ambient temperature and bundling math shown above). For the final termination sizing and breaker selection, you must drop back down to the 60°C or 75°C column, depending on the rating printed on your breakers and receptacles. The 90°C rating of THHN is essentially a thermal buffer that protects the wire when bundled or in hot environments, but the lugs it connects to will melt or degrade if subjected to 90°C heat.
How do aluminum wire chart amps compare to copper?
Aluminum has higher resistance than copper, requiring a larger physical cross-section to carry the same current. For example, to achieve the same ampacity as 2 AWG Copper (115A at 75°C), you must use 1/0 AWG Aluminum (120A at 75°C). Aluminum is highly cost-effective for large feeder cables (like 200A service entrance conductors or subpanel feeders), but it requires specific anti-oxidant paste (like Noalox) and torque-rated lugs to prevent loose connections and arcing over time. You can find detailed aluminum vs copper load comparisons via resources like Electrical Technology's Wire Size Calculator.
Does the ground wire count in the wire chart amps derating?
No. According to NEC 310.15(C)(1), equipment grounding conductors (the bare copper or green insulated wires) are not considered 'current-carrying conductors' for the purpose of bundling derating. They only carry current during a fault condition, which should trip the breaker instantly. However, if you are running multi-wire branch circuits (MWBC) with shared neutrals, the neutral does count as a current-carrying conductor if it carries unbalanced load or harmonic currents, which will trigger the derating multipliers.
