Conductor ampacity is not a single current rating attached to a wire size. It depends on conductor material, insulation temperature rating, installation conditions, and connected equipment. For example, 6 AWG copper has reference ampacities of 55 A, 65 A, and 75 A in the 60°C, 75°C, and 90°C columns of NEC Table 310.16. Those values are different starting points—not three interchangeable circuit ratings.
Use the tables below to identify base ampacity, then establish which temperature column and installation rules apply. A table lookup alone does not select the breaker, establish the permitted load, or complete the conductor design.
Reference Basis and Table Conditions
The reference values below are selected entries from NFPA 70, National Electrical Code, 2023 edition, Table 310.16, as reproduced in HELUKABEL’s Allowable Ampacity Tables. They are NEC-based values, not IEC current-carrying capacities. The manufacturer’s reproduction is a reference aid rather than the adopted code text; confirm the edition, amendments, table notes, and applicable permissions in the code adopted for the project.
Table 310.16 applies to insulated conductors in raceway, cable, or earth, including directly buried installations, under these base conditions:
| Condition | Reference basis |
|---|---|
| Conductor voltage rating | Up to and including 2,000 V |
| Conductor temperature rating | 60°C, 75°C, or 90°C, as applicable |
| Ambient temperature | 30°C, equivalent to 86°F |
| Current-carrying conductors | Not more than three |
| Material | Copper, or aluminum/copper-clad aluminum, using the appropriate material column |
The table title and notes identify the installation and conductor-count conditions. Ambient temperatures other than 30°C require consideration of the applicable correction factors; more than three current-carrying conductors require consideration of the adjustment rules and their exceptions. These conditions are part of the lookup, not optional refinements.
The voltage range describes the table’s application; it does not change a particular product’s voltage rating. For example, Southwire’s SPEC 10000 THHN/THWN-2 copper product is rated 600 V even though its published ampacities reference NEC Table 310.16.
Copper Conductor Ampacity Reference
All values are amperes. These are selected sizes, not the complete Table 310.16. Temperature headings refer to conductor temperature ratings, not ambient temperatures.
| Conductor size | 60°C / 140°F | 75°C / 167°F | 90°C / 194°F |
|---|---|---|---|
| 14 AWG* | 15 | 20 | 25 |
| 12 AWG* | 20 | 25 | 30 |
| 10 AWG* | 30 | 35 | 40 |
| 8 AWG | 40 | 50 | 55 |
| 6 AWG | 55 | 65 | 75 |
| 4 AWG | 70 | 85 | 95 |
| 3 AWG | 85 | 100 | 115 |
| 2 AWG | 95 | 115 | 130 |
| 1 AWG | 110 | 130 | 145 |
| 1/0 AWG | 125 | 150 | 170 |
| 2/0 AWG | 145 | 175 | 195 |
| 3/0 AWG | 165 | 200 | 225 |
| 4/0 AWG | 195 | 230 | 260 |
| 250 kcmil | 215 | 255 | 290 |
| 300 kcmil | 240 | 285 | 320 |
| 350 kcmil | 260 | 310 | 350 |
| 400 kcmil | 280 | 335 | 380 |
| 500 kcmil | 320 | 380 | 430 |
Source: HELUKABEL, Allowable Ampacity Tables, identified as NFPA 70: NEC–2023, Table 310.16, copper section. Southwire’s SPEC 10000 independently publishes the same 75°C and 90°C values for the corresponding listed copper sizes.
* Small-conductor overcurrent protection limits must be checked separately. A 12 AWG copper entry of 30 A in the 90°C column does not authorize a general-purpose 30 A branch circuit. Southwire explicitly notes the NEC 240.4(D) limits of 15 A for 14 AWG copper, 20 A for 12 AWG copper, and 30 A for 10 AWG copper; application-specific provisions can modify the general protection rules.
Aluminum and Copper-Clad Aluminum Ampacity Reference
All values are amperes. Table 310.16 groups aluminum and copper-clad aluminum in the same ampacity section. That grouping does not establish that a particular terminal or piece of equipment accepts either material.
| Conductor size | 60°C / 140°F | 75°C / 167°F | 90°C / 194°F |
|---|---|---|---|
| 12 AWG* | 15 | 20 | 25 |
| 10 AWG* | 25 | 30 | 35 |
| 8 AWG | 35 | 40 | 45 |
| 6 AWG | 40 | 50 | 55 |
| 4 AWG | 55 | 65 | 75 |
| 3 AWG | 65 | 75 | 85 |
| 2 AWG | 75 | 90 | 100 |
| 1 AWG | 85 | 100 | 115 |
| 1/0 AWG | 100 | 120 | 135 |
| 2/0 AWG | 115 | 135 | 150 |
| 3/0 AWG | 130 | 155 | 175 |
| 4/0 AWG | 150 | 180 | 205 |
| 250 kcmil | 170 | 205 | 230 |
| 300 kcmil | 195 | 230 | 260 |
| 350 kcmil | 210 | 250 | 280 |
| 400 kcmil | 225 | 270 | 305 |
| 500 kcmil | 260 | 310 | 350 |
Source: HELUKABEL, Allowable Ampacity Tables, identified as NFPA 70: NEC–2023, Table 310.16, aluminum or copper-clad aluminum section.
* The source table directs users to NEC 240.4(D) for small-conductor overcurrent protection limitations, except where modified elsewhere in the Code. Do not apply the copper protection limits above to aluminum or copper-clad aluminum merely because the AWG number matches.
Confirm conductor-material compatibility, permitted wire size, and any solid/stranded restrictions from the equipment markings and installation instructions. UL’s circuit-breaker application guide identifies these as separate termination markings; an ampacity table cannot supply them.
Choosing the Temperature Column
Establish the conductor’s rating for its actual environment
Use the conductor marking and the product documentation to determine the applicable insulation rating. A product with several type designations may have different permitted temperatures in different environments.
For example, Southwire SPEC 10000 states:
- THHN: 90°C in dry locations.
- THWN-2: 90°C in wet or dry locations.
- For that product, exposure to oil limits the THWN-2 application to 75°C.
Those are documented conditions for that product, not permission to assign 90°C to every conductor described informally as “THHN.”
The column temperature is also not a prediction that the conductor will operate at exactly that temperature. It identifies the temperature basis of the tabulated ampacity.
Establish the equipment termination limit separately
A conductor with 90°C insulation does not automatically qualify for its 90°C table ampacity at equipment terminals. UL explains that higher-temperature insulation may be used, but wire sizing must respect the temperature rating marked on the circuit breaker. Panelboard and connected-device markings must also be considered.
For a conductor connected to equipment with a confirmed 75°C termination basis, the 75°C table value is the relevant termination ampacity limit. If another connected termination imposes a 60°C basis, that lower limit must also be addressed.
Do not use the temperature marking on a loose lug as a substitute for the rating of the equipment assembly. Schneider Electric’s Wire Temperature Ratings and Terminations, Bulletin 0110DB9901R2/02, explains that a 90°C-rated lug installed in equipment rated for 60°C or 75°C conductors does not raise the equipment’s termination rating. This bulletin explains the thermal relationship; its older code references are not a substitute for the project’s adopted edition.
Keep insulation requirements and ampacity limits distinct
Equipment can require a minimum insulation temperature while still requiring wire sizing from a lower-temperature ampacity column. “Use 90°C wire” and “use the 90°C ampacity” are different instructions.
Likewise, a 60/75°C marking does not mean that every wire connected to the equipment has the same allowable current. The conductor rating, equipment listing, permitted wire range, and applicable installation rules still determine the usable combination.
How Base Ampacity, Correction Factors, and Terminal Limits Relate
Keep two values separate:
- The conductor ampacity after applicable ambient-temperature correction and conductor-count adjustment.
- The ampacity limit associated with the equipment termination temperature basis.
Where the conductor’s higher insulation rating is permitted as the starting point for correction and adjustment, calculate from that column and then compare the result with the termination limit. Schneider Electric describes this comparison directly: use the smaller value.
For a Table 310.16 application with confirmed inputs, the relationship can be expressed as:
[
I_{\text{adjusted}}=I_{\text{base}}\times F_T\times F_N
]
[
I_{\text{thermal limit}}=\min\left(I_{\text{adjusted}},I_{\text{termination}}\right)
]
Where:
- (I_{\text{base}}) is the table ampacity for the conductor material, size, and applicable insulation temperature rating, in amperes.
- (F_T) is the applicable ambient-temperature correction factor, dimensionless.
- (F_N) is the applicable current-carrying-conductor adjustment factor, dimensionless.
- (I_{\text{termination}}) is the table ampacity corresponding to the permitted termination temperature basis for that conductor, in amperes.
- (I_{\text{thermal limit}}) is the lower result of these two thermal checks, before other applicable restrictions.
This expression does not replace cable-specific requirements, exceptions, or circuit-specific sizing rules. It explains why choosing the lowest temperature column at the start of every calculation can be unnecessarily restrictive, while using only the highest column can overstate the permitted ampacity.
The factors must come from the applicable code tables and conditions. HELUKABEL’s NEC–2023 reproduction identifies Table 310.15(B)(1)(1) for ambient correction based on 30°C and Table 310.15(C)(1) for adjustment associated with more than three current-carrying conductors. Count conductors under the applicable rules rather than treating every wire in the raceway as automatically current-carrying.
Example: 6 AWG Copper With 90°C Insulation and 75°C Terminations
Assume the following hypothetical conditions:
| Input | Assumed condition or source |
|---|---|
| Material and size | 6 AWG copper |
| Applicable insulation rating | Confirmed 90°C for the installation environment |
| Termination basis | Confirmed 75°C at connected equipment |
| Ambient temperature | 40°C |
| Current-carrying conductors | Six, with the adjustment rule applicable and no exception used |
| Other restrictions | None introduced for this limited comparison |
The 90°C base ampacity is 75 A. The 75°C termination-column ampacity is 65 A. For 40°C ambient and 90°C insulation, the reproduced correction table gives 0.91; for four through six current-carrying conductors, the adjustment table gives 0.80.
[
I_{\text{adjusted}}=75\times0.91\times0.80=54.6\text{ A}
]
[
I_{\text{thermal limit}}=\min(54.6,65)=54.6\text{ A}
]
The correction-and-adjustment result controls this comparison. The result is not a 55 A equipment rating or an instruction to install a particular breaker.
Under otherwise identical conditions at 30°C with no conductor-count adjustment required, the comparison would instead be:
[
\min(75,65)=65\text{ A}
]
In that case, the termination limit controls. The 90°C insulation provides a higher starting value for applicable corrections; it does not remove the 75°C termination limit.