Amps Wire Gauge Chart: NEC 310.16 Ampacity Reference Guide

For standard residential branch circuits, the direct answer is simple: use 14 AWG copper for 15A circuits, 12 AWG for 20A, and 10 AWG for 30A. However, once you move past basic branch circuits into feeders, subpanels, or high-temperature environments, guessing wire size becomes a fire hazard. The definitive amps wire gauge chart used by electricians in the United States is derived from National Electrical Code (NEC) Table 310.16.

How to read this table: The chart below is divided by conductor material (Copper vs. Aluminum) and then by temperature rating (60°C, 75°C, and 90°C). The values represent the maximum allowable ampacity (current-carrying capacity) for a single, isolated conductor in an ambient air temperature of 30°C (86°F). Before you pull any wire, you must identify which temperature column your specific terminals and breakers support, and then apply any necessary derating factors for conduit fill or ambient heat.

The Master Amps Wire Gauge Chart (NEC Table 310.16)

The following data-dense table reflects the standard ampacities for copper and aluminum conductors. Source standard: NEC Article 310.16 (formerly 310.15(B)(16)), assuming not more than three current-carrying conductors in a raceway and an ambient temperature of 30°C.

Which Column Applies to Your Installation?

The most common mistake DIYers make when using an amps wire gauge chart is looking at the 90°C column because they bought THHN wire, which is stamped with a 90°C rating on the jacket. In almost all residential scenarios, you cannot use the 90°C column for your final breaker sizing.

Here is the decision framework for selecting the correct column:

• The 60°C Column (Small Branch Circuits): Per NEC 240.4(D), small conductors are strictly capped. 14 AWG is limited to 15A, 12 AWG to 20A, and 10 AWG to 30A. Even if your 12 AWG THHN wire is technically rated for 30A at 90°C, the breaker cannot exceed 20A. Always use the 60°C column for 14, 12, and 10 AWG copper.
• The 75°C Column (Feeders and Large Branches): For 8 AWG and larger, modern circuit breakers, lugs, and terminal bars are manufactured and tested to handle 75°C. If you are wiring a 50A hot tub or a 100A subpanel feeder, size your wire using the 75°C column.
• The 90°C Column (Derating Only): The 90°C ampacity is almost exclusively used as the starting baseline for calculating derating adjustments (explained below). You calculate the derated 90°C value, but the final result must still be protected by a breaker sized according to the 60°C or 75°C limits.

Derating Factors: When the Chart Lies to You

The ampacities in the chart above assume ideal conditions: a single conductor in free air, or no more than three current-carrying conductors in a conduit, at an ambient temperature of 30°C (86°F). If your installation deviates from this, the chart's base values are dangerously optimistic.

According to NEC Article 310.15(C)(1), when you bundle multiple current-carrying conductors together in a single raceway, the heat they generate cannot dissipate. You must apply a derating multiplier to the wire's 90°C ampacity.

Real-World Derating Example:
Imagine you are pulling wire for a multi-wire branch circuit and a dedicated 20A circuit through the same 3/4-inch EMT conduit. You have 4 current-carrying conductors in the pipe. You decide to use 12 AWG THHN copper.

1. Look at the 90°C column for 12 AWG Copper: 30 Amps.
2. Consult the derating table for 4-6 conductors: The adjustment factor is 80%.
3. Multiply: 30A × 0.80 = 24 Amps.
4. Because 24A is greater than the 20A breaker you plan to use, 12 AWG THHN is perfectly legal and safe for this bundled run.

If you had 10 current-carrying conductors in that conduit, the derating factor drops to 50%. Your 12 AWG wire would derate to 15A (30A × 0.50), meaning you could no longer use it on a 20A breaker; you would be forced to upsize to 10 AWG.

Ambient Temperature Correction: If you are running NM-B cable through an attic in a southern climate where temperatures routinely hit 120°F (49°C), you must apply a temperature correction factor. At 120°F, the correction factor for 90°C insulation is roughly 0.82. A 60A feeder might suddenly only be rated for 49A, requiring an upsized wire.

What This Chart Cannot Tell You (Voltage Drop & Beyond)

An amps wire gauge chart is strictly a thermal limit chart—it tells you the point at which the wire's insulation will melt or degrade. It tells you absolutely nothing about power quality or physical installation constraints.

1. Voltage Drop

If you run 10 AWG copper to a 30A RV pedestal 150 feet away, the wire will not overheat, but the voltage at the receptacle might drop below 110V under load. This can damage compressor motors in RV air conditioners. The NEC recommends keeping voltage drop under 3% for branch circuits and 5% total for feeder plus branch. For long runs, use a dedicated voltage drop calculator and upsize your wire by one or two gauges, regardless of what the ampacity chart permits.

2. Conduit Fill Capacity

Just because 10 AWG wire has the ampacity to handle your load doesn't mean you can physically pull four of them through a 1/2-inch PVC conduit. NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires to prevent jamming and insulation damage during the pull. Always check conduit fill tables before buying your raceway.

3. Short-Circuit Let-Through Energy

Ampacity charts assume steady-state continuous loads. They do not account for the massive magnetic and thermal forces generated during a dead short. While a 14 AWG wire might be protected by a 15A breaker for normal overloads, the breaker must clear a 5,000A fault fast enough to prevent the 14 AWG wire from vaporizing. This is why you cannot arbitrarily downsize wire just because the continuous load is low; the wire must be thermally robust enough to survive the fraction of a second before the breaker trips.