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Copper conductor ampacity NOM-001

Ampacity is the maximum electric current that a copper conductor can carry continuously under specific installation conditions without its temperature exceeding the insulation design limit.

Ampacity table for copper conductors at 90 °C

Section titled “Ampacity table for copper conductors at 90 °C”

The values apply to copper conductors with insulation rated for a maximum operating temperature of 90 °C (e.g., THHN, XHHW‑2) in installations with no more than three current-carrying conductors in a raceway or cable, and an ambient temperature of 30 °C / 86 °F, according to NOM‑001‑SEDE.

AWG / kcmil Size Cross‑Sectional Area (mm² / kcmil) Diameter (mm / in) Ampacity (A)
14 2.08 mm² / 4.11 kcmil 1.63 mm / 0.0641 in 25
12 3.31 mm² / 6.53 kcmil 2.05 mm / 0.0808 in 30
10 5.26 mm² / 10.4 kcmil 2.59 mm / 0.102 in 40
8 8.36 mm² / 16.5 kcmil 3.26 mm / 0.129 in 55
6 13.3 mm² / 26.2 kcmil 4.11 mm / 0.162 in 75
4 21.1 mm² / 41.7 kcmil 5.19 mm / 0.204 in 95
3 26.7 mm² / 52.6 kcmil 5.83 mm / 0.229 in 110
2 33.6 mm² / 66.4 kcmil 6.54 mm / 0.258 in 130
1 42.4 mm² / 83.7 kcmil 7.35 mm / 0.289 in 150
1/0 53.5 mm² / 106 kcmil 8.25 mm / 0.325 in 170
2/0 67.4 mm² / 133 kcmil 9.27 mm / 0.365 in 195
3/0 85.0 mm² / 168 kcmil 10.4 mm / 0.410 in 225
4/0 107 mm² / 212 kcmil 11.7 mm / 0.460 in 260
250 kcmil 127 mm² / 250 kcmil 12.7 mm / 0.500 in 290
300 kcmil 152 mm² / 300 kcmil 13.9 mm / 0.548 in 320
350 kcmil 177 mm² / 350 kcmil 15.0 mm / 0.591 in 350
400 kcmil 203 mm² / 400 kcmil 16.1 mm / 0.633 in 380
500 kcmil 253 mm² / 500 kcmil 18.0 mm / 0.707 in 430
600 kcmil 304 mm² / 600 kcmil 19.7 mm / 0.775 in 475
750 kcmil 380 mm² / 750 kcmil 22.0 mm / 0.866 in 535
1000 kcmil 507 mm² / 1000 kcmil 25.4 mm / 1.000 in 615

Temperature correction factors

Section titled “Temperature correction factors”

For ambient temperatures other than 30 °C / 86 °F, the following correction factors shall be applied to the tabulated ampacity. The values are valid for conductors with 90 °C insulation.

Ambient temperature (°C / °F) Correction factor
21 – 25 °C / 69.8 – 77.0 °F 1.08
26 – 30 °C / 78.8 – 86.0 °F 1.00
31 – 35 °C / 87.8 – 95.0 °F 0.91
36 – 40 °C / 96.8 – 104.0 °F 0.82
41 – 45 °C / 105.8 – 113.0 °F 0.71
46 – 50 °C / 114.8 – 122.0 °F 0.58
51 – 55 °C / 123.8 – 131.0 °F 0.41

Grouping correction factors

Section titled “Grouping correction factors”

When more than three current-carrying conductors are installed in the same raceway or cable, the ampacity must be multiplied by the indicated factors.

Number of current-carrying conductors Correction factor
1 – 3 1.00
4 – 6 0.80
7 – 9 0.70
10 – 20 0.50
21 – 30 0.45
31 – 40 0.40
41 or more 0.35

Corrected ampacity calculation

Section titled “Corrected ampacity calculation”

The corrected ampacity of a conductor is obtained by multiplying the tabulated ampacity by the temperature and grouping correction factors.

Icorr = Itable × FT × FA

where:

Variable Description Unit
Icorr Corrected ampacity A
Itable Tabulated ampacity for 90 °C and 30 °C ambient A
FT Temperature correction factor -
FA Grouping correction factor -

Calculation example

Section titled “Calculation example”

A 10 AWG copper conductor with THHN insulation (90 °C) is installed in a raceway with 5 current-carrying conductors, in an ambient of 40 °C / 104 °F.

  • Itable = 40 A
  • FT for 40 °C = 0.82
  • FA for 4‑6 conductors = 0.80
  • Icorr = 40 A × 0.82 × 0.80 = 26.24 A

The resulting corrected ampacity is 26.24 A.

Frequently Asked Questions (FAQ)

Section titled “Frequently Asked Questions (FAQ)”

What is the ampacity of a 12 AWG copper conductor with THHN insulation (90 °C) for fewer than three conductors in a raceway according to NOM‑001?

Section titled “What is the ampacity of a 12 AWG copper conductor with THHN insulation (90 °C) for fewer than three conductors in a raceway according to NOM‑001?”

The basic ampacity is 30 A when no more than three conductors are used and the ambient temperature remains at 30 °C / 86 °F.

How is the ampacity of a 10 AWG copper conductor at 90 °C reduced when the ambient temperature reaches 45 °C?

Section titled “How is the ampacity of a 10 AWG copper conductor at 90 °C reduced when the ambient temperature reaches 45 °C?”

A correction factor of 0.71 is applied, reducing the tabulated ampacity from 40 A to 28.4 A.

What grouping factor corresponds to 8 current-carrying conductors in the same metallic raceway?

Section titled “What grouping factor corresponds to 8 current-carrying conductors in the same metallic raceway?”

The grouping factor is 0.70, so the ampacity of each conductor must be multiplied by 0.70.

What is the corrected ampacity of a 6 AWG copper conductor at 90 °C with an ambient temperature of 35 °C and 5 active conductors in the raceway?

Section titled “What is the corrected ampacity of a 6 AWG copper conductor at 90 °C with an ambient temperature of 35 °C and 5 active conductors in the raceway?”

Itable = 75 A, FT = 0.91, FA = 0.80, resulting in 75 × 0.91 × 0.80 = 54.6 A.

What size copper conductor with 90 °C insulation is required to carry a corrected current of 100 A considering a total correction factor of 0.65?

Section titled “What size copper conductor with 90 °C insulation is required to carry a corrected current of 100 A considering a total correction factor of 0.65?”

The minimum required tabulated ampacity is 100 A / 0.65 = 153.8 A, therefore a 1/0 AWG conductor with an ampacity of 170 A is selected.

What is the maximum operating temperature that defines the 90 °C column in NOM‑001 and its equivalent in Fahrenheit?

Section titled “What is the maximum operating temperature that defines the 90 °C column in NOM‑001 and its equivalent in Fahrenheit?”

The maximum insulation operating temperature is 90 °C / 194 °F.

References

Section titled “References”