Choose the ampacity column from the permitted conductor and terminal temperatures, not just the insulation printed on the wire. Under 2020 NEC 110.14(C), a 90°C conductor connected to 75°C equipment terminals does not automatically get the 90°C ampacity. The terminal limit still applies.
Watch Victor explain the 100-amp rule
Open 110.14(C), then Table 310.16. Victor explains how the equipment rating affects the temperature column you use.
Watch Victor explain the 100-amp ruleWatch the existing JCR lesson on YouTubeStart with the equipment ratings
The general termination rules are:
| Equipment or circuit | Default temperature basis |
|---|---|
| 100A or less, or equipment marked for 14 AWG through 1 AWG | 60°C, unless listed and identified for a different permitted use |
| Over 100A, or equipment marked for conductors larger than 1 AWG | 75°C, subject to the equipment and conductor ratings |
Exactly 100 amps belongs in the “100A or less” group. Many modern terminals are identified for 75°C conductors. Read the equipment markings and instructions at both ends. Do not assume the default or the higher rating.
Example: 6 AWG copper
2020 NEC Table 310.16 gives these base ampacities for 6 AWG copper under the table’s stated conditions:
| 60°C | 75°C | 90°C |
|---|---|---|
| 55A | 65A | 75A |
For 90°C-rated individual conductors in raceway with 75°C-rated terminations at both ends, the termination limit is 65A, before any further reduction required by the installation. The 75A value in the 90°C column does not override those terminals. Southwire’s conductor data also shows the 65A and 75A values.
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See CE courses and class datesWhen can you use the 90°C column?
You can use the permitted insulation temperature for ampacity correction and adjustment. Then compare the result with the terminal limit and any wiring-method restriction.
Example: assume 6 AWG copper, 90°C insulation, 75°C terminations and a required 80% adjustment factor, with no other correction. Start with 75A × 0.80 = 60A. The terminal limit is 65A, so the resulting allowable ampacity is 60A.
Work another example in our temperature correction and ampacity adjustment guide.
Common questions
Can NM-B cable use the 75°C column?
2020 NEC 334.80 limits NM cable ampacity to the 60°C value. Its 90°C conductor rating can be used for adjustment and correction, but the final ampacity cannot exceed the 60°C limit. A 75°C breaker terminal does not remove that cable rule.
Does a 90°C lug marking make the whole equipment 90°C rated?
No. Follow the equipment’s listing and instructions. A replacement lug’s marking alone does not change the rating of the complete assembly.
Can I put 6 AWG copper on any 65A load?
No. You still need the wiring method, terminal ratings, load calculation, adjustment factors and overcurrent rules. Dwelling service and feeder allowances are another separate check (see our 310.12 guide).
Keep practicing
Try our most-missed NEC mock exam questions and 2020 NEC practice questions. For each missed answer, find the section in your code book, read the rule and work the question again.
Reviewed October 25, 2026, for the 2020 NEC. Use the edition required by your licensing exam. Follow the adopted code and local amendments on the job.
