Wire Ampacity Chart and Wire Size Chart

This page puts the three charts electricians and inspectors use most in one place: the NEC Table 310.16 ampacity chart, a wire size chart by breaker, and the Table 310.12 dwelling service chart. Below them are the four rules that decide which number you are allowed to use.

Wire ampacity chart (NEC Table 310.16)

Allowable ampacities, NEC Table 310.16 (2023), not more than three current-carrying conductors, 30°C ambient. 240.4(D) limits overcurrent protection to 15 A for 14 AWG, 20 A for 12 AWG and 30 A for 10 AWG copper (15 A for 12 AWG and 25 A for 10 AWG aluminum).

The 60°C column covers insulation types such as TW and UF. The 75°C column covers THW, THWN, XHHW and USE. The 90°C column covers THHN, THWN-2, XHHW-2 and RHW-2. A conductor with 90°C insulation is not automatically allowed its 90°C ampacity: the terminations decide (see below).

Wire size chart by breaker size

Smallest conductor whose Table 310.16 ampacity meets the breaker rating, before voltage drop, ambient or bundling corrections. The 75°C column applies only when every termination is rated 75°C.

Each amperage links to a detailed page: 15 A · 20 A · 30 A · 40 A · 50 A · 60 A · 100 A service · 100 A subpanel · 125 A · 150 A · 200 A service.

Dwelling service chart (Table 310.12)

NEC Table 310.12: single-phase 120/240 V dwelling services and feeders that carry the entire load of the dwelling (the 83% rule).

Table 310.12 applies only to single-phase, 120/240 V services and to feeders that carry the entire load of a dwelling unit. It does not apply to a feeder to a subpanel that serves only part of the house, to commercial buildings, or to three-phase services. In those cases, size from Table 310.16.

Four rules that decide which number you can use

1. The termination rating (110.14(C)). For circuits of 100 A or less, or conductors 14 through 1 AWG, use the 60°C column unless every termination is listed for 75°C. Above 100 A, use the 75°C column unless the equipment says otherwise. Most modern breakers and panels are rated 60/75°C.

2. The cable type. NM-B and UF cables are limited to the 60°C ampacity (334.80, 340.80), even though NM-B conductors are 90°C-rated. SE cable used as an interior branch circuit or feeder follows 338.10(B)(4).

3. Small-conductor limits (240.4(D)). Regardless of the table, overcurrent protection may not exceed 15 A for 14 AWG copper, 20 A for 12 AWG copper and 30 A for 10 AWG copper (15 A and 25 A for 12 and 10 AWG aluminum).

4. Conditions of use. The table assumes 30°C (86°F) ambient and no more than three current-carrying conductors. Hotter locations need a correction factor (Table 310.15(B)(1)), and more than three current-carrying conductors need an adjustment factor (310.15(C)(1)). You may start the adjustment from the 90°C column, but the final result may not exceed the ampacity allowed at the terminations.

Which column applies? Quick decision table

Single conductors in free air, such as overhead spans, use Table 310.17 rather than 310.16. Neither table applies to flexible cords, which use Table 400.5(A)(1).

Worked example: 100 A feeder to a detached garage

A 100 A, 120/240 V feeder in PVC conduit, 75°C terminations, 90 feet long.

• Table 310.12 does not apply (the garage panel doesn't carry the entire dwelling load).
• From Table 310.16, 75°C column: 3 AWG copper (100 A) or 1 AWG aluminum (100 A).
• Equipment grounding conductor (Table 250.122, 100 A): 8 AWG copper or 6 AWG aluminum.
• Voltage drop at 80 A actual load, 1 AWG aluminum: (2 × 21.2 × 80 × 90) ÷ 83,690 = 3.65 V, or 1.5%. Good.

Worked example: same load, three different answers

An air handler has 36 A of electric heat, which runs as a continuous load. The branch circuit must be sized at 125%: 36 × 1.25 = 45 A, and 45 A is a standard breaker size (240.6(A)). The smallest conductor rated at least 45 A depends on the column:

• NM-B cable (60°C): 8 AWG copper is only 40 A, so 6 AWG copper (55 A).
• THHN in conduit, 75°C terminations: 8 AWG copper (50 A).
• Aluminum at 75°C: 8 AWG aluminum is 40 A, so 6 AWG aluminum (50 A).

The equipment's nameplate MCA and MOCP take priority over this arithmetic where they're given; they already include the 125% factor.

Common mistakes when reading the chart

• Taking the 90°C value as the answer for THHN, when the terminals are rated 75°C.
• Using Table 310.12 for a subpanel feeder, a commercial service or a three-phase service.
• Ignoring 240.4(D) and reading 14 AWG copper at 20 A or 12 AWG at 25 A from the 75°C column.
• Skipping the correction for rooftop, attic or high-ambient runs, or for more than three current-carrying conductors in a raceway. Use Tables 310.15(B)(1) and 310.15(C)(1).
• Forgetting that aluminum needs a larger size for the same ampacity, typically two gauge numbers (10 AWG copper vs. 8 AWG aluminum at 30 A, 3 AWG vs. 1 AWG at 100 A).

Frequently asked questions

What size wire is rated for 100 amps?

3 AWG copper or 1 AWG aluminum at 75°C per Table 310.16. For a dwelling service or main feeder, Table 310.12 permits 4 AWG copper or 2 AWG aluminum.

What is the ampacity of 10 AWG copper?

30 A at 60°C, 35 A at 75°C and 40 A at 90°C, but the breaker is limited to 30 A by 240.4(D).

How many amps can 12 gauge wire carry?

Table 310.16 lists 12 AWG copper at 20 A (60°C), 25 A (75°C) and 30 A (90°C), but 240.4(D) limits its breaker to 20 A. See 20 amp wire size.

What is the ampacity of 4/0 aluminum?

180 A at 75°C. That's why it serves a 200 A dwelling service under Table 310.12 (which only needs 166 A), but a 200 A subpanel feeder needs 250 kcmil aluminum. See 200 amp service wire size.

Why can't I use the 90°C column for THHN?

You can use it as the starting point for derating, but the final ampacity is limited by the lowest temperature rating of any termination, which is usually 60°C or 75°C.

Does the 2026 NEC change these values?

Table 310.16 remains the reference table for conductor ampacity; always confirm against the edition your jurisdiction enforces.

Related

• Wire Size Calculator
• Wire Gauge Chart (AWG)
• Voltage Drop Calculator

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Values from NEC 2023 Tables 310.16, 310.12 and 250.122. Last updated: October 6, 2026. This chart is a reference; the NEC edition adopted by your jurisdiction governs. Electrical work should be done by qualified people.