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

The wire amps chart—formally known as an ampacity table—dictates the maximum continuous current a conductor can carry before its insulation begins to thermally degrade. For standard residential copper wire in a 30°C (86°F) ambient environment, the baseline numbers are straightforward: 14 AWG is rated for 15A, 12 AWG for 20A, 10 AWG for 30A, and 6 AWG for 55A to 65A depending on the temperature column. However, pulling the right number from the chart requires understanding your termination ratings, ambient temperatures, and conduit fill.

How to Read This Wire Amps Chart

The table below is sourced directly from NEC Table 310.16 (National Electrical Code, NFPA 70), which is the definitive standard for conductor ampacities in the United States. The chart is divided by conductor material (Copper vs. Aluminum) and insulation temperature ratings (60°C, 75°C, and 90°C). Bookmark the quick-jump rows below for the most frequently queried residential and light-commercial wire sizes.

For deeper reference on material properties, the Copper Development Association provides extensive data on how copper's thermal conductivity outperforms aluminum in tight conduit spaces.

Which Temperature Column Applies to Your Installation

The most common mistake DIYers and junior electricians make is defaulting to the 90°C column because modern THHN/THWN-2 wire is stamped with a 90°C rating. You cannot use the 90°C column for final breaker sizing unless every single termination in the circuit is also rated for 90°C.

Per NEC 110.14(C), the allowable ampacity is determined by the lowest temperature rating of any connected device, termination, or conductor in the circuit. Here is how to select your column:

• The 60°C Column: Use this for almost all residential branch circuits rated 100A or less. Standard breakers, receptacles, and wire nuts are typically rated for 60°C or 75°C, but NEC 240.4(D) strictly limits small conductors (14, 12, and 10 AWG) to 15A, 20A, and 30A respectively, effectively locking them into the 60°C column limits regardless of insulation.
• The 75°C Column: Use this for feeders, subpanels, and service entrances rated over 100A. Most modern lugs in load centers and large breakers are explicitly marked 75°C.
• The 90°C Column: Use this almost exclusively as the starting baseline for derating calculations (explained below), not for final ampacity.

How Derating Modifies These Base Ampacities

The wire amps chart assumes two things: an ambient air temperature of 30°C (86°F), and no more than three current-carrying conductors bundled together in a raceway or conduit. When you violate either assumption, the wire cannot dissipate heat as efficiently, and you must apply a derating factor.

According to NFPA 70 (NEC) Table 310.15(C)(1), if you pull 4 to 6 current-carrying conductors through a single conduit, you must multiply the wire's base ampacity by 80%. For 7 to 9 conductors, the factor drops to 70%.

Note that ambient temperature derating (NEC Table 310.15(B)(1)) uses the same 90°C baseline. If your conduit runs across a 110°F attic, you multiply the 90°C ampacity by the 87% temperature correction factor before applying any bundling derating.

What This Wire Amps Chart Cannot Tell You

While the NEC 310.16 wire amps chart is the law of the land for thermal limits, it is not a complete design tool. It will not tell you:

1. Voltage Drop: A 12 AWG wire is rated for 20A whether it is 10 feet long or 300 feet long. However, at 300 feet, a 16A continuous load will cause severe voltage drop, starving your equipment. Always calculate voltage drop separately for runs over 100 feet.
2. Short-Circuit Let-Through Current: Ampacity dictates continuous thermal limits. It does not tell you how the wire will react to a 10,000A short-circuit fault before the breaker trips. That requires checking the breaker's AIC (Ampere Interrupting Capacity) rating and the wire's short-circuit withstand curve.
3. Physical Pulling Limits: The chart ignores mechanical stress. Pulling 4/0 AWG aluminum through a conduit with multiple 90-degree sweeps requires calculating pulling tension and sidewall bearing pressure to avoid stretching or tearing the conductor.

Frequently Asked Questions