AWG Cable Sizing Chart: NEC Ampacity & Breaker Matching Guide

For standard residential branch circuits, the baseline AWG cable sizes are: 14 AWG for 15 amps, 12 AWG for 20 amps, 10 AWG for 30 amps, 8 AWG for 40 amps, and 6 AWG for 55 amps. These values assume copper conductors in a standard 30°C (86°F) ambient environment with no more than three current-carrying conductors bundled together. Sizing wire correctly is not just about matching the breaker; it requires cross-referencing insulation temperature ratings and applying correction factors as defined in NEC Table 310.16.

How to Read the NEC 310.16 Ampacity Table

The National Electrical Code (NEC) Table 310.16 provides the allowable ampacities for insulated conductors. Before looking at the numbers, you must understand how the table is structured. The table is divided into temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). These columns do not represent the temperature of the wire during operation; they represent the thermal limit of the wire's insulation material before it begins to degrade or melt.

Complete AWG Cable Ampacity & Breaker Chart

The following spec-sheet-table maps the raw ampacity data from NEC 310.16 (2020/2023 editions) to the maximum standard overcurrent protection device (breaker) sizes permitted by NEC 240.4(B). This table assumes copper conductors.

*Note: NEC 240.4(B) allows rounding up to the next standard breaker size if the calculated load does not exceed the conductor ampacity, and the next standard size does not exceed 800A. However, for 2 AWG and 4/0 AWG, specific load calculations dictate whether you round up or stay at the lower standard size.

Which Temperature Column Applies to Your Installation?

A common mistake on the jobsite is looking at the 90°C column for THHN wire and assuming you can push 90 amps through a 3 AWG wire. You cannot. The applicable column is dictated by the "weakest link" rule found in NEC 110.14(C).

You must use the temperature column that matches the lowest temperature rating of any connected device, termination, or conductor in the circuit. Here is how that breaks down in practice:

• Use the 60°C Column when: You are using NM-B (Romex) cable. Even if the NM-B contains 90°C rated THHN conductors inside, NEC 334.80 strictly limits the ampacity of NM-B to the 60°C column. You also use this column for any circuit rated 100A or less where the equipment termination temperature is not explicitly marked (default assumption for older or unmarked gear).
• Use the 75°C Column when: You are pulling individual THHN/THWN-2 wires in conduit, and terminating them on modern breakers, lugs, and receptacles that are explicitly marked "75°C" or "AL/CU". Almost all modern residential panels and breakers are rated for 75°C terminations.
• Use the 90°C Column when: You are calculating derating factors (explained below). The 90°C column is almost never used for final termination ampacity in residential work; it exists primarily to give you a higher mathematical baseline before applying penalty factors for heat and bundling.

Derating Factors: When Your Base Ampacity Drops

The ampacity values in the main table assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors (CCCs) in a raceway. When you exceed these parameters, the wire cannot shed heat efficiently, and you must derate (reduce) the allowable ampacity.

Derating modifies the base value using the 90°C column as the starting point, regardless of your termination limits. You multiply the 90°C ampacity by the correction factor found in NEC Table 310.15(C)(1) for bundling, or Table 310.15(B)(1) for ambient temperature.

Decision Path: Pick Your Exact AWG Cable

Stop guessing and use this decision-tree-table to select the exact wire type and gauge for your specific project. This path assumes standard residential 120/240V split-phase power and copper conductors unless aluminum is specified.

What This Table Cannot Tell You

While NEC 310.16 is the bible for thermal ampacity, it is not a complete design tool. Relying solely on this table will lead to failures in three specific scenarios:

1. Voltage Drop on Long Runs: The NEC ampacity table does not account for resistance over distance. A 12 AWG wire can safely carry 20 amps indefinitely without melting, but if that wire is 250 feet long, the voltage at the far end will drop below 114V under load, causing motors to overheat and electronics to brown out. For runs over 100 feet, always calculate voltage drop (aim for <3% on branch circuits) and upsize the AWG accordingly. Refer to the Southwire Voltage Drop Calculator for exact math.
2. Conduit Fill Capacity: Table 310.16 tells you how much current a wire can carry, but NEC Chapter 9, Table 1 dictates how many wires physically fit inside a conduit. You cannot stuff twelve 10 AWG THHN wires into a 1/2-inch EMT conduit, regardless of derating math. You must cross-reference conduit fill tables to ensure you can actually pull the wires without damaging the insulation.
3. Short-Circuit Let-Through Current (AIC): Ampacity handles continuous thermal loads. It does not tell you if the wire can survive the magnetic and thermal stress of a 10,000-amp short circuit before the breaker trips. For standard residential work, standard THHN/NM-B is sufficient, but in commercial or industrial settings with high fault currents, you must verify the equipment's AIC rating and ensure the conductor bracing is adequate.

For deeper code analysis and installation scenarios, the EC&M National Electrical Code section provides excellent ongoing interpretations of how these tables apply to modern edge cases like solar inverters and EV chargers. Always verify your final AWG cable selection against your local Authority Having Jurisdiction (AHJ), as local amendments can supersede baseline NEC guidance.