AWG Wire Size Chart Amps: NEC 310.16 Reference & Derating Guide

When sizing a circuit, the direct answer for maximum current capacity lies in the AWG wire size chart for amps, specifically governed by NEC Table 310.16. For standard residential copper branch circuits, 14 AWG handles 15 amps, 12 AWG handles 20 amps, and 10 AWG handles 30 amps. However, these baseline numbers assume specific temperature ratings and installation conditions that, if ignored, will result in overheated conductors and tripped breakers.

The Master AWG Wire Size Chart (Amps & AWG)

How to read this table: The rows represent the American Wire Gauge (AWG) physical size of the copper conductor. The columns represent the insulation temperature rating (60°C, 75°C, and 90°C). The ampacity values listed assume copper conductors, an ambient air temperature of 30°C (86°F), and no more than three current-carrying conductors bundled in a single raceway or cable. Data is sourced directly from the National Fire Protection Association (NFPA) NEC Table 310.16.

Which Temperature Column Applies to Your Installation?

The most common mistake made when reading an AWG wire size chart for amps is blindly selecting the 90°C column because modern THHN wire is physically rated for it. In practice, the allowable ampacity is almost always limited by the terminations, not the wire insulation.

Under NEC 110.14(C), the temperature rating of the wire must be matched to the lowest temperature rating of any connected device, terminal, or splice. Most standard residential circuit breakers, receptacles, and switches are rated for 75°C. However, NEC 240.4(D) introduces a hard restriction for small conductors: circuits rated 100 amps or less using 14, 12, or 10 AWG wire must use the 60°C column for overcurrent protection sizing, regardless of the wire's actual insulation rating.

Real-World Example: You are wiring a 20A receptacle circuit using 12 AWG THHN (90°C rated). Looking at the chart, the 90°C column shows 30A. The 75°C column shows 25A. But because the circuit is under 100A and uses 12 AWG, NEC 240.4(D) forces you to the 60°C column, which caps the ampacity at 20A. You must protect this wire with a 20A breaker, not a 25A or 30A breaker.

You only get to use the 75°C column for circuits over 100A (like a 200A main feeder using 4/0 copper, which allows 230A instead of 195A) or for specific high-temperature industrial equipment explicitly marked otherwise. For 99% of home branch circuits, default to the 60°C column.

Derating Factors: When the Base Chart Fails You

The baseline AWG wire size chart assumes ideal conditions: 30°C ambient temperature and a maximum of three current-carrying conductors in a conduit. When you deviate from these conditions, you must apply derating factors. Derating modifies the base value by applying a percentage multiplier to the 90°C column (even if your final termination limit is 60°C), and then comparing the result to your termination column limit. The final allowable ampacity is the lower of the two numbers.

Bundling Derating (NEC Table 315.15(C)(1))

When current flows through a wire, it generates heat. If you bundle 4 to 6 current-carrying conductors in a single conduit, they cannot dissipate heat effectively. You must multiply the base 90°C ampacity by 80%. For 7 to 9 conductors, the multiplier drops to 70%.

Ambient Temperature Derating (NEC Table 310.15(B)(1))

If your conduit runs through a hot attic in the summer, the ambient temperature might hit 40°C (104°F) or 50°C (122°F). At 40°C, you multiply the 90°C ampacity by 0.91. At 50°C, the multiplier drops to 0.82.

Worked Numeric Example: You are pulling four 12 AWG THHN wires (two hots, one neutral, one ground — the ground does not count as current-carrying, leaving 3 current-carrying conductors) through an attic conduit that reaches 40°C (104°F).
1. Base 90°C ampacity for 12 AWG = 30A.
2. Bundling: 3 conductors means no bundling derating (multiplier 1.0).
3. Temperature: 40°C ambient requires a 0.91 multiplier.
4. Math: 30A × 1.0 × 0.91 = 27.3A.
5. Final Check: 27.3A is greater than the 60°C termination limit of 20A. Therefore, you can still safely use this wire on a standard 20A breaker. If the attic hit 60°C (multiplier 0.71), the derated value would be 21.3A, which still passes the 20A termination check, but leaves virtually zero thermal headroom.

What the Table Cannot Tell You

The AWG wire size chart for amps only solves for thermal limits (preventing the insulation from melting). It completely ignores voltage drop. According to the Copper Development Association, a 10 AWG copper wire carrying 30A over a 200-foot run will experience a voltage drop of roughly 7.5% on a 120V circuit. This exceeds the recommended 3% maximum, causing motors to run hot and lights to dim. For long runs, you must upsize the wire based on voltage drop calculators, not just the thermal ampacity chart. Furthermore, the chart does not dictate physical conduit fill limits; you must consult NEC Chapter 9, Table 1 to ensure your wires physically fit inside the PVC or EMT conduit without jamming.

Standard Breaker to Minimum Copper AWG Pairings

For quick planning on standard 120V/240V residential branch circuits (using NM-B Romex or THHN in conduit at standard 30°C ambient temperatures), use this comparison matrix. This assumes copper conductors and standard 60°C termination rules for circuits 100A and under.

Remember that the 'Max Continuous Load' column applies to loads expected to run for 3 hours or more (like an EV charger or a space heater). NEC 210.20(A) requires the breaker to be sized at 125% of the continuous load, which mathematically limits a 20A breaker to 16A of continuous draw. For non-continuous loads (like a toaster or a vacuum), you can pull the full rated amperage of the breaker.