11.2 Termination Temperature Limitations
Key Takeaways
- NEC 110.14(C) requires conductor sizing at terminations to respect the temperature rating of the equipment terminals, not only the conductor insulation rating.
- For equipment rated 100 A or less, or marked for conductors 1 AWG and smaller, use the 60°C column unless the equipment is listed and marked for a higher temperature.
- For equipment rated over 100 A, or marked for conductors larger than 1 AWG, the 75°C column is generally permitted unless marked otherwise.
- 90°C insulation (such as THHN) may be used for derating starting values when allowed, but the final selected ampacity still cannot exceed the termination temperature limit.
- Mixed terminations on a circuit are governed by the lowest applicable termination rating unless the installation is engineered and listed for a higher rating.
Terminations Set the Real Limit
Quick Answer: Even when a conductor’s insulation is rated 90°C, NEC 110.14(C) often forces you to size the circuit using the 60°C or 75°C ampacity column because that is what the equipment terminals are rated for. On the Arkansas JW exam, “THHN is 90°C” is incomplete unless you also check the termination temperature.
Heat at a lug, breaker stab, or device terminal can damage equipment long before the conductor insulation in the middle of a raceway fails. That is why the NEC separates conductor insulation temperature rating from termination temperature limitations. Table 310.16 may list three ampacities for one conductor size; 110.14(C) tells you which of those numbers you may use when connecting to equipment.
110.14(C) Decision Framework
Equipment 100 A or less / conductors 1 AWG and smaller
Unless the equipment is listed and marked otherwise, conductors are selected from the 60°C column of Table 310.16 (or equivalent). This rule catches a huge share of branch-circuit and small-feeder work: 15–100 A panels, disconnects, and devices that are not marked 75°C. A stem that says “panelboard marked 60°C only” or simply describes unmarked 60 A equipment is steering you to the 60°C column for final size.
Equipment over 100 A / conductors larger than 1 AWG
Unless marked otherwise, conductors are generally selected from the 75°C column. Many commercial feeders land here. Do not assume 90°C termination ampacity just because the wire is THHN or XHHW-2; most standard equipment is still 75°C at the lugs.
Higher than 75°C terminations
Using ampacity above the 75°C column at a termination requires equipment listed and identified for the higher temperature. On exam day, that almost always appears as an explicit marking in the stem. If the stem is silent, do not invent a 90°C termination rating.
Insulation Rating vs Termination Rating
These two ratings interact but answer different questions:
| Question | What controls it |
|---|---|
| May I install this insulation type in this location? | Article 310 / insulation listing (dry, damp, wet) |
| What ampacity may I start with for adjustment/correction? | Often the insulation temperature column (commonly 90°C for THHN) when the code allows |
| What ampacity must the chosen conductor satisfy at the lug? | 110.14(C) termination temperature |
| What breaker may I use on 14/12/10 AWG? | Often 240.4(D), separate from both |
A classic Arkansas-style trap: eight current-carrying 12 AWG copper THHN conductors need adjustment. You may begin adjustment from the 90°C ampacity (30 A) because the insulation is 90°C-rated. After applying the adjustment factor, you still verify that the conductor is acceptable under the termination column (often 60°C = 20 A for small equipment) and under 240.4(D). Passing the derating math does not repeal the terminal limit.
Worked Examples
Example A — 40 A circuit, 60°C terminations
A 40 A noncontinuous load lands on equipment marked only 60°C. Conductors are copper THHN in EMT, three CCC, 30°C ambient. THHN’s 90°C table ampacity for 8 AWG is 55 A, and the 75°C value is 50 A, but the terminations require the 60°C value. 8 AWG copper at 60°C is 40 A, which meets the 40 A load. Choosing 8 AWG because “THHN is 55 A” without checking 60°C terminations is the wrong reasoning even if the size happens to work.
Example B — 225 A feeder, 75°C lugs
A feeder calculated at 210 A (already including continuous-load multipliers) terminates on a breaker and lugs rated 75°C. Copper conductors are THHN. You need a conductor whose 75°C ampacity is at least 210 A. 4/0 AWG copper is 230 A at 75°C and 260 A at 90°C. The 90°C number is useful if you later derate, but the installed size must still clear 230 A at 75°C. Selecting based only on 90°C could undersize relative to the lugs if adjustment brings you below the termination requirement.
Example C — Mixed equipment ratings
If one end of a conductor terminates on 60°C equipment and the other on 75°C equipment, the 60°C limit governs that conductor’s required ampacity unless a listed exception applies. The circuit is only as strong as its hottest-vulnerable termination.
Pressure Connectors, Dissimilar Metals, and Markings
110.14 also expects terminations to be made with connectors identified for the conductor material (copper, aluminum, or Cu/Al dual-rated) and for the temperature. Aluminum terminations typically need connectors listed for aluminum and proper preparation. Exam stems that mention “Cu only” lugs reject aluminum even when ampacity tables would otherwise allow an aluminum size.
When equipment is marked 60/75°C, you may use the 75°C column for conductor sizing when the conductors are so rated — that marking is the green light 110.14(C) looks for. No marking on ≤100 A equipment usually means stay in the 60°C column.
Arkansas JW Timing Tip
On a timed NEC 2023 open-book exam, flip first to the equipment rating in the stem, then to Table 310.16. Candidates who open 310.16 first and grab the largest column waste time and miss 110.14(C). Write a two-line habit in your code-book margin: (1) termination column for final ampacity, (2) insulation column for derating start only when permitted. That habit alone recovers multiple ampacity items on the Arkansas journeyman exam.
A 60 A circuit uses copper THHN and terminates on equipment rated 100 A or less with no higher-temperature marking. Which Table 310.16 column generally governs final conductor selection under 110.14(C)?
Copper THHN conductors have 90°C insulation, but the equipment terminals are rated 75°C. How should the 90°C ampacity column be treated?
A feeder over 100 A lands on equipment marked for 75°C terminations. The stem does not identify any 90°C-rated equipment. Which statement is correct?