Wire Ampacity Chart: Copper and Aluminum (NEC Table 310.16)

Copper conductors: amperes by temperature rating (NEC 2023)

NEC 2023 also lists 18 AWG and 16 AWG copper, in the 90 °C column only (14 A and 18 A). The lookup and this chart start at 14 AWG, the smallest copper size for general wiring (NEC 2023 310.3(A)).

Before you use these values

• The terminals decide the column: circuits of 100 A or less, and equipment marked for 14 AWG to 1 AWG conductors, use the 60 °C column unless the equipment is listed and marked for 75 °C; circuits over 100 A, and equipment marked for conductors larger than 1 AWG, use 75 °C (NEC 2023 110.14(C)(1)).
• The 90 °C column is a starting point for correcting and adjusting a 90 °C conductor; the result may not exceed the column of the lowest-rated termination (NEC 2023 110.14(C)).
• More than three current-carrying conductors together, or an ambient above 30 °C, lowers these values. Ampacity derating calculator
• Services and main feeders of dwellings at 120/240 V, 100 A to 400 A, may be sized at 83 % of their rating under NEC 2023 310.12 instead; this chart does not apply it.
• Single conductors in open air have their own, higher values (NEC 2023 310.17).
• THHN is rated 90 °C in dry and damp locations, THWN 75 °C in dry and wet locations, and THWN-2 90 °C in dry and wet locations (NEC 2023 Table 310.4(1)).
• Verify against the edition your AHJ enforces.

Aluminum conductors: amperes by temperature rating (NEC 2023)

Before you use these values

• The aluminum columns also cover copper-clad aluminum (NEC 2023 Table 310.16).
• The terminals decide the column: circuits of 100 A or less, and equipment marked for 14 AWG to 1 AWG conductors, use the 60 °C column unless the equipment is listed and marked for 75 °C; circuits over 100 A, and equipment marked for conductors larger than 1 AWG, use 75 °C (NEC 2023 110.14(C)(1)).
• The 90 °C column is a starting point for correcting and adjusting a 90 °C conductor; the result may not exceed the column of the lowest-rated termination (NEC 2023 110.14(C)).
• More than three current-carrying conductors together, or an ambient above 30 °C, lowers these values. Ampacity derating calculator
• Services and main feeders of dwellings at 120/240 V, 100 A to 400 A, may be sized at 83 % of their rating under NEC 2023 310.12 instead; this chart does not apply it.
• Single conductors in open air have their own, higher values (NEC 2023 310.17).
• THHN is rated 90 °C in dry and damp locations, THWN 75 °C in dry and wet locations, and THWN-2 90 °C in dry and wet locations (NEC 2023 Table 310.4(1)).
• Verify against the edition your AHJ enforces.

Smallest conductor for common circuit ratings

Before you use these values

• The terminals decide the column: circuits of 100 A or less, and equipment marked for 14 AWG to 1 AWG conductors, use the 60 °C column unless the equipment is listed and marked for 75 °C; circuits over 100 A, and equipment marked for conductors larger than 1 AWG, use 75 °C (NEC 2023 110.14(C)(1)).
• A continuous load needs conductors and an overcurrent device for 125 % of it (NEC 2023 210.19(A)(1) and NEC 2023 210.20(A)); look up that current instead.
• A marked cell is a small conductor that NEC 2023 240.4(D) does not allow behind a device of that rating; the wire size calculator moves on to the first size it allows.
• More than three current-carrying conductors together, or an ambient above 30 °C, can call for a larger size. Ampacity derating calculator
• A long run can need a larger size to keep the voltage drop down. Voltage drop calculator
• Services and main feeders of dwellings at 120/240 V, 100 A to 400 A, may be sized at 83 % of their rating under NEC 2023 310.12 instead; this table does not apply it.

How it’s calculated

I_table

the table ampacity in amperes, for up to three current-carrying conductors, 30 °C ambient

I_required

the current you enter under Required Ampacity

Copper starts at 14 AWG and aluminum at 12 AWG, the smallest sizes NEC 2023 310.3(A) allows for general wiring; the table gives aluminum no value below that.

The first size in the list is marked “Smallest”. The lookup applies no terminal rating, no 125 % for continuous loads, no 240.4(D) limit and no derating; the wire size calculator applies all four.

Assumptions

• Every value is for up to three current-carrying conductors in a raceway, a cable or the earth, at 30 °C (86 °F) ambient. More conductors or a hotter ambient lower it.
• Conductors rated up to 2000 V, the range the table covers.
• Copper or aluminum. Copper-clad aluminum reads the aluminum columns.
• The lookup reads the table only: terminals, continuous loads, 240.4(D) and derating are left to you or to the wire size calculator.
• Sizes from 14 AWG to 2000 kcmil; the smaller copper rows of the table are only mentioned under the copper chart.
• Whole amperes, as the table lists them.
• Single conductors in open air (NEC 2023 310.17), dwelling services sized under NEC 2023 310.12 and manufacturer ratings are not covered.

Worked example

Code references

Section numbers are from NEC 2023 (NFPA 70). This page explains them in its own words and quotes no code text.

• NEC 2023 Table 310.16: ampacities by size, metal and temperature column, for up to three current-carrying conductors, 30 °C ambient
• NEC 2023 110.14(C)(1): which column the terminals allow when the equipment is not marked for a higher one
• NEC 2023 110.14(C): the column is limited by the lowest-rated termination; a higher-rated conductor may start from its own column for correction and adjustment
• NEC 2023 240.4(D): the largest overcurrent device for small copper and aluminum conductors
• NEC 2023 240.6(A): the standard overcurrent-device ratings, the rows of the reverse table
• NEC 2023 310.3(A): the smallest copper and aluminum sizes for general wiring
• NEC 2023 210.19(A)(1): branch-circuit conductors: the noncontinuous load plus 125 % of the continuous load
• NEC 2023 215.2(A)(1): feeder conductors: the same 125 % rule
• NEC 2023 210.20(A): the overcurrent device: the same 125 % rule
• NEC 2023 Article 100: a continuous load is one whose maximum current is expected to last 3 hours or more
• NEC 2023 Table 310.15(B)(1)(1): correction factors for an ambient other than 30 °C
• NEC 2023 Table 310.15(C)(1): how much the ampacity drops when one raceway or cable holds more than three current-carrying conductors
• NEC 2023 310.12: dwelling services and main feeders (120/240 V, 100 A to 400 A) sized at 83 % of their rating (not applied here)
• NEC 2023 310.17: single conductors in open air, with higher values than Table 310.16
• NEC 2023 Table 310.4(1): insulation temperature ratings, e.g. THHN, THWN and THWN-2
• NEC 2023 334.80: NM cable uses the 60 °C ampacity; the 90 °C value may be the starting point for derating

Read the NEC on NFPA’s free access page

Why answers online disagree

• A different column

  A chart that prints one number per size has picked a column for you, often 75 °C or 90 °C. 12 AWG copper is 20 A, 25 A and 30 A depending on the column, and the terminals decide which one counts.

  Check: which temperature column the other chart used.

• An older code book

  Several cells differ from older editions, among them 6 AWG aluminum at 90 °C (55 A here), 600 kcmil copper at 60 °C (350 A here), 800 kcmil aluminum at 90 °C (445 A here) and 2000 kcmil copper at 60 °C (555 A here). A chart copied from an older book can show another value there or elsewhere.

  Check: which edition the chart follows.

• Another table

  NEC 2023 310.17 gives higher values for single conductors in open air, NEC 2023 310.12 sizes some dwelling services and main feeders at 83 % of their rating, and manufacturers publish tables for their own cables and conditions.

  Check: which table and which conditions the chart is based on.

• Chassis-wiring charts

  Charts for chassis or point-to-point wiring in electronics list much higher currents for the same gauge, for short wires in open air. They do not apply to building wiring.

  Check: that the chart is meant for building wiring under the NEC.

• NM cable

  NM cable is held to the 60 °C ampacity; the 90 °C value only serves as the starting point for derating (NEC 2023 334.80). A chart listing 12 AWG NM at 30 A reads the wrong column.

  Check: the wiring method.

• Copper-clad aluminum

  Copper-clad aluminum reads the aluminum columns. A chart that groups it with copper overstates it.

  Check: the conductor metal.

• Ampacity is not the breaker size

  NEC 2023 240.4(D) caps the overcurrent device for small conductors whatever their ampacity: copper 14 AWG 15 A, 12 AWG 20 A and 10 AWG 30 A; aluminum 12 AWG 15 A and 10 AWG 25 A. 12 AWG copper has 30 A in the 90 °C column but still takes a device of 20 A at most — except where NEC 2023 240.4(E) or NEC 2023 240.4(G) sends the circuit elsewhere, as motor and air-conditioning circuits go to Articles 430 and 440.

  Check: 240.4(D) before picking a breaker.

Questions

Related calculators

• Wire size calculator

  Size a 50 A circuit with terminals, continuous load, 240.4(D) and derating applied.

• Ampacity derating calculator

  Nine current-carrying 12 AWG copper conductors rated 90 °C in one raceway, corrected and adjusted.

• Voltage drop calculator

  Check a long run once the size carries the current.