AWG Stranded Wire Chart: Ampacity, Sizing, and NEC Derating Guide

For standard residential and commercial branch circuits using stranded THHN/THWN-2 copper wire, you will almost always use the 75°C column for final breaker sizing and the 90°C column for ampacity derating, per NEC Table 310.16. Stranded wire offers superior flexibility for pulling through conduit, but its ampacity limits are strictly governed by the temperature ratings of your terminations, not just the wire insulation itself.

How to Read This AWG Stranded Wire Chart

The data below is sourced directly from the National Electrical Code (NEC) Table 310.16. Before you pick a wire gauge, you must understand the three temperature columns. Modern stranded building wire (like THHN/THWN-2) features insulation rated for 90°C. However, the circuit breakers, lugs, and receptacles you connect that wire to are typically only rated for 75°C (or sometimes 60°C for older/specific devices).

The NEC enforces a 'weakest link' rule: your final allowable ampacity cannot exceed the temperature rating of the lowest-rated component in the circuit. Therefore, the 90°C column is primarily used as a starting point for mathematical derating, while the 75°C column dictates your final breaker size.

The Complete AWG Stranded Copper Ampacity Table

The following table applies to copper conductors with insulation types rated up to 90°C (THHN, THWN-2, XHHW-2) installed in a raceway or cable, with an ambient temperature of 30°C (86°F).

Which Column Applies to Your Installation?

A frequent and costly mistake on the jobsite is sizing the breaker using the 90°C column. If you run 10 AWG THHN (40A at 90°C) and put it on a 40A breaker, you are violating code if your breaker lugs are only rated for 75°C (which almost all standard residential breakers under 100A are). The 75°C column limits 10 AWG to 35A, meaning you must use a 35A or 30A breaker.

How Derating Modifies Your Base Ampacity

The base numbers in the table above assume you have no more than three current-carrying conductors in a single raceway (conduit) and an ambient temperature of 30°C (86°F). If you pull multiple circuits through the same pipe, the wires heat each other up. This is where the 90°C column saves the day.

Per NEC 310.15(C)(1), when you have 4 to 6 current-carrying conductors in a raceway, you must derate the wire's ampacity to 80% of its base value. Because THHN is rated 90°C, you apply this 80% penalty to the 90°C column, not the 75°C column.

Worked Numeric Example:

• You are pulling two 240V circuits (4 hot wires total) through a single 3/4-inch EMT conduit.
• You want to use 10 AWG stranded THHN for a 30A circuit.
• Look at the 90°C column for 10 AWG: 40A.
• Apply the 80% derating factor: 40A × 0.80 = 32A.
• Compare the derated value (32A) to the 75°C termination limit (35A). You must use the lower of the two: 32A.
• Since 32A is greater than your 30A load and breaker size, 10 AWG is legally compliant. If you had incorrectly applied the derating to the 75°C column (35A × 0.8 = 28A), you would have falsely concluded you needed to upsize to 8 AWG.

What This Table Cannot Tell You

An ampacity chart is only half the sizing equation. Relying on it blindly will lead to three specific field failures:

1. Voltage Drop: The NEC table assumes a short run. If you are running a 50A EV charger 150 feet from the panel using 6 AWG stranded wire, the ampacity is fine, but your voltage drop will exceed the recommended 3% limit. You must upsize to 4 AWG or 3 AWG strictly to maintain voltage stability, regardless of ampacity.
2. Physical Lug Fit: Stranded wire has a larger overall outside diameter than solid wire of the same AWG due to the air gaps between the strands. A 6 AWG solid wire might slide easily into a compact 50A GFCI breaker lug, but 6 AWG stranded might be too thick to seat properly without trimming strands (which is a code violation and a fire hazard). Always verify the physical lug capacity.
3. Short-Circuit Let-Through Current: The chart tells you what the wire can carry continuously without melting its insulation. It does not tell you how it will withstand the magnetic and thermal stresses of a 10,000A short-circuit event before the breaker trips. That is governed by the breaker's interrupting rating and the wire's specific short-circuit withstand data.

Decision Path: Pick Your Wire Size

Use this decision tree to finalize your stranded wire purchase. Follow the steps sequentially to arrive at a concrete gauge.

For exact physical dimensions of the strands and overall diameters to ensure conduit fill compliance, cross-reference your pick with the Engineering Toolbox AWG dimensional data. Always verify your final design against local AHJ (Authority Having Jurisdiction) amendments, as local inspectors may have specific preferences for stranded versus solid wire in residential branch circuits.