Copper Wire Chart Amps: NEC 310.16 Ampacity Reference & Sizing Guide

When sizing a branch circuit or feeder, the baseline copper wire chart amps are dictated by NEC Table 310.16. For standard residential and commercial copper wiring, the baseline ampacities are: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A (or 50A at 75°C), 6 AWG = 55A (or 65A at 75°C), and 4 AWG = 70A (or 85A at 75°C). However, the number you can legally use depends entirely on the insulation temperature rating, the termination limits of your breaker, and the specific installation method.

How to Read the NEC Copper Wire Ampacity Chart

The ampacity table below is sourced directly from NFPA 70 (National Electrical Code) Table 310.16. It assumes copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors in a raceway or cable.

To use this chart correctly, you must understand the three temperature columns:

• 60°C (140°F) Column: Use this for non-metallic sheathed cable (NM-B / Romex) and any termination rated strictly for 60°C. This is the default column for most residential branch circuits up to 100 amps.
• 75°C (167°F) Column: Use this for individual THHN/THWN wires pulled through conduit, as well as most modern breaker panel lugs and commercial terminations rated for 75°C.
• 90°C (194°F) Column: THHN wire is manufactured with 90°C insulation, but you almost never use this column for final ampacity. The 90°C column is strictly used as the starting baseline for calculating derating factors (like bundling or high ambient heat) before applying the termination temperature limit.

* Asterisks denote sizes restricted by NEC 240.4(D) overcurrent protection limits.

Quick-Jump: Most Queried Copper Wire Sizes

For fast bench reference, here are the most common residential and light-commercial circuit requirements based on standard 60°C/75°C terminations:

• 15-Amp Lighting/Receptacle Circuit: 14 AWG Copper (Minimum), 12 AWG recommended for voltage drop mitigation on long runs.
• 20-Amp Kitchen/Bathroom Appliance Circuit: 12 AWG Copper (Strict minimum per code).
• 30-Amp Dryer / RV Receptacle: 10 AWG Copper.
• 40-Amp / 50-Amp Range or EV Charger: 8 AWG Copper (for 40A/50A at 75°C terminations). Note: 50A EV chargers often require 6 AWG if the manufacturer specifies a continuous load derating.
• 60-Amp Subpanel Feeder: 6 AWG Copper (at 75°C) or 4 AWG Copper (if using 60°C NM-B cable).
• 100-Amp Subpanel Feeder: 3 AWG Copper (at 75°C).
• 200-Amp Service Entrance / Main Feeder: 2/0 AWG Copper.

How Derating Modifies Base Ampacity (And What the Table Misses)

The numbers in the copper wire chart above assume ideal conditions. In the real world, Electrical Contractor Magazine and NEC Article 310.15 frequently require you to reduce (derate) those baseline numbers based on two main factors:

1. Bundling (More than 3 Current-Carrying Conductors)

When you pull more than three current-carrying conductors through a single conduit, the wires heat each other up. You must apply a derating factor from NEC Table 310.15(C)(1). Crucial rule: You apply this derating factor to the 90°C column, not the 60°C or 75°C column.

Worked Example: You are pulling four current-carrying 6 AWG THHN copper wires through an EMT conduit to a subpanel.
1. Look at the 90°C column for 6 AWG: 75A.
2. Look at the derating table for 4-6 conductors: 80%.
3. Multiply: 75A × 0.80 = 60A.
4. Check termination limits: Your breaker lugs are rated 75°C. The 75°C column for 6 AWG is 65A. Since your derated value (60A) is lower than the termination limit (65A), your final allowable ampacity is 60A. You can protect this with a 60A breaker.

2. Ambient Temperature

If your conduit runs through an attic or outdoors where the ambient temperature exceeds 30°C (86°F), you must apply a temperature correction factor, again starting from the 90°C column.

What the Table Cannot Tell You

The ampacity chart is blind to two critical physical realities:

• Voltage Drop: NEC Table 310.16 does not account for distance. A 10 AWG copper wire is rated for 30A, but if you run it 150 feet to a 240V load, you will experience a voltage drop exceeding the recommended 3% threshold. For long runs, you must upsize the wire (e.g., to 8 AWG or 6 AWG) purely to maintain voltage stability, even if the breaker size remains the same.
• Conduit Fill: The chart tells you the electrical limit, but not the physical limit. You must calculate conduit fill percentage (NEC Chapter 9, Table 1) to ensure the wires will physically fit and dissipate heat without jamming during the pull.

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