Cable AWG Amperage Chart: NEC Table 310.16 Sizing Guide

The exact cable AWG amperage depends on three physical variables: the wire gauge (AWG), the conductor material (copper vs. aluminum), and the insulation temperature rating. To size a circuit correctly, you cannot simply memorize a single number for a given wire size. Instead, you must cross-reference the wire gauge with the correct temperature column in the National Electrical Code (NEC) Table 310.16, then apply correction factors for your specific installation environment.

How to read this chart: The rows represent the American Wire Gauge (AWG) size. The columns are split by conductor material (Copper or Aluminum) and then by the insulation's maximum temperature rating (60°C, 75°C, or 90°C). The values inside the cells represent the maximum allowable ampacity—the continuous current the wire can carry without degrading the insulation—assuming an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled in a raceway.

The Master Cable AWG Amperage Chart (NEC Table 310.16)

Below is the complete reference table for the most common residential and commercial wire sizes. Bookmark this section for quick lookups on the jobsite. Data is sourced directly from the NFPA 70 National Electrical Code.

Which Temperature Column Actually Applies to Your Install?

The most common mistake DIYers and junior apprentices make is looking at a spool of 90°C rated THHN wire, finding the 90°C column in the table above, and sizing their breaker based on that higher number. This violates NEC Article 110.14(C), which governs terminal temperature limitations.

The rule is simple: the weakest link in the circuit dictates your allowable ampacity. You must use the temperature column that matches the lowest-rated component in your entire run. This includes the wire insulation, the breaker terminals, the lugs in your subpanel, and the receptacles.

• The 60°C Column: Use this for 14, 12, and 10 AWG circuits (NEC 110.14(C)(1)(a) mandates this for circuits rated 100A or less, unless the equipment is specifically marked otherwise). You also use this if you are terminating on older equipment, certain cheap receptacles, or NM-B (Romex) cable, which is inherently limited to 60°C ampacities regardless of the wire's actual insulation.
• The 75°C Column: This is the modern standard for circuits over 100A, and for most 15A-50A circuits where the equipment (like Square D QO or Eaton BR breakers) is explicitly marked '75°C' on the terminal lug. Most modern THWN-2 wire in conduit is terminated using this column.
• The 90°C Column: You almost never use this column for your final breaker sizing because standard breakers and lugs are not rated for 90°C. The 90°C column is used strictly as a starting point for derating calculations (explained below).

Derating Factors: When the Base Chart Lies

The cable AWG amperage values in Table 310.16 assume ideal conditions: an ambient air temperature of 30°C (86°F) and no more than three current-carrying conductors (CCCs) in a single conduit. When real-world conditions deviate from this, the wire's ability to shed heat drops, and you must derate the ampacity.

1. Ambient Temperature Correction
If you are pulling wire through a hot attic in the summer, the ambient temperature might hit 40°C (104°F) or higher. You must multiply the base ampacity by a correction factor. For example, if you are using 10 AWG THHN (90°C insulation) in a 40°C attic, you look at the 90°C column (40A) and multiply by the 40°C correction factor for 90°C wire (0.91). 40A × 0.91 = 36.4A. However, because your termination is likely limited to 60°C or 75°C, you must then compare this derated 90°C value to the 60°C/75°C column limits and use the lowest resulting number.

2. Bundling (More than 3 CCCs)
When you bundle multiple circuits in a single conduit, the wires heat each other up. If you have 4 to 6 current-carrying conductors in a raceway, you must multiply the base ampacity by 80%. If you have 7 to 9 CCCs, the multiplier drops to 70%.

What the Ampacity Table Cannot Tell You

While the NEC table is the legal baseline for preventing wire fires, it is purely a thermal limit chart. It does not account for several critical engineering realities that will cause your installation to fail or perform poorly if ignored.

Voltage Drop
Table 310.16 does not care if your 12 AWG wire is 15 feet long or 400 feet long; the ampacity remains 20A. But at 400 feet, a 16A load on 12 AWG copper will result in a voltage drop of roughly 10 volts (over 8%). The Southwire voltage drop guidelines and NEC informational notes recommend keeping voltage drop under 3% for branch circuits and 5% for the total feeder-plus-branch run. For long runs to a detached garage or a well pump, you must upsize the wire purely for voltage drop, even if the ampacity table says the smaller wire is thermally safe.

Physical Lug Fit and Bend Radius
According to the chart, 4/0 AWG copper has an ampacity of 230A at 75°C, making it theoretically perfect for a 200A residential service feeder. However, 4/0 wire is incredibly stiff. Many 200A main breaker lugs physically cannot accept a 4/0 conductor, or the wire cannot be bent to the required radius inside a standard 24-inch panel enclosure without stressing the termination. Always check the manufacturer's lug sizing data sheet before pulling large gauge feeders; you may need to use a 250 kcmil aluminum wire (which is more flexible and fits larger lugs) or install a junction gutter to transition wire sizes.

Short-Circuit Withstand Ratings
Ampacity defines continuous thermal limits. It does not tell you what happens during a 10,000A dead short. The wire must be able to withstand the thermal and magnetic forces of a fault current for the milliseconds it takes the breaker's magnetic trip to clear the fault. This requires checking the I²t (let-through energy) of your specific breaker and comparing it to the short-circuit withstand rating of the cable, a calculation that goes beyond basic ampacity charts and into protective device coordination.