Checked against primary sources 2026-08-24

A 90 degree conductor is still a 90 degree conductor. You just cannot use all of it

The section does not change what the wire can carry. It changes which column of the ampacity table you are allowed to read the answer out of, and that is a narrower thing than most people carry in their heads.

What is actually being limited

The conductor. The lug. The breaker. Each has a temperature rating, and the ampacity you are permitted to use is coordinated to the lowest of them (NEC 110.14(C)).

Read that carefully, because the wording is doing something precise. A 90 degree conductor does not become a 75 degree conductor. Its insulation is unchanged and so is its ampacity. What the section restricts is the number you are allowed to carry forward when you size against the load and the overcurrent device.

That distinction is why the same conductor can be worth two different figures in the same problem. Its ampacity, corrected and adjusted, is one number. The ampacity you may use at the terminations is another, read out of a lower column with no factors applied to it. Both are real and the smaller one wins.

The hundred ampere threshold

One number splits the section, and it splits it two ways at once.

• Circuits rated 100 amperes or less, or equipment marked for 14 AWG through 1 AWG conductors, default to the 60 degree column.
• Circuits rated over 100 amperes, or equipment marked for conductors larger than 1 AWG, default to the 75 degree column.

The word "or" in each of those is what catches people. The ampere rating is one trigger and the conductor marking on the equipment is a separate, independent trigger. A 100 ampere panel whose terminals are marked 14 AWG through 1 AWG lands in the first case twice over. A 60 ampere disconnect whose lugs are marked for conductors larger than 1 AWG lands in the second on the marking alone, even though its ampere rating would have said otherwise.

So when a stem tells you the terminal marking, that is not scenery. It is one of the two ways into the rule and it can override the reading you would have taken from the ampere rating.

The ways out of the default column

Both subdivisions permit a conductor with a higher temperature rating. What they control is which column its ampacity gets read from.

On the 100 amperes or less side

A 60 degree conductor is permitted outright. A higher rated conductor is permitted too, with its ampacity determined from the 60 degree column of the ampacity table. A higher rated conductor may be used at its own higher column only where the equipment is listed and identified for use with conductors of that rating.

There is a fourth option and it is the one candidates have never read. For motors marked with design letter B, C or D, conductors rated 75 degrees or higher are permitted, with the ampacity not exceeding the 75 degree value. A motor stem that names a design letter is pointing at this option.

On the over 100 amperes side

A 75 degree conductor is permitted outright. A higher rated conductor is permitted with its ampacity held to the 75 degree column, or at its own rating where the equipment is listed and identified for use with such conductors.

Separately installed pressure connectors

Connectors bought and installed apart from the equipment carry their own listing, and the conductor is used at an ampacity no greater than the connector is listed for. This is the route by which a 90 degree termination is genuinely available, and it is a listing question rather than a wire question.

Marked is not the same as listed and identified

A temperature number stamped near a terminal does not on its own let you move up a column. The permission in the section attaches to equipment listed and identified for use with conductors of that rating, and the general rule applies unless the equipment is listed and marked otherwise.

In practice that means the instructions and the listing, not the casting. Most ordinary breakers, panelboards, safety switches and receptacles are 75 degree equipment at best, and a great deal of small equipment is 60 degree equipment no matter what insulation you feed it with.

On an exam this shows up as a stem that mentions a 90 degree insulation type and then describes perfectly ordinary equipment. Nothing in it says listed and identified, so nothing in it permits the 90 degree column.

What the 90 degree rating is genuinely worth

Correction for ambient and adjustment for conductor count are applied to the ampacity at the conductor's own rating, and the section says in its own opening that a conductor rated higher than the termination is permitted to be used that way.

So the value of 90 degree insulation is headroom to lose. You start from a bigger number and the factors eat into it before anything else does. In a hot roof or a full raceway that is often the difference between one trade size and the next.

It buys nothing at all when there is no derating to do. Three conductors at normal ambient landing on 75 degree lugs get the 75 degree figure whether the insulation is rated 75 or 90, and the extra rating has done no work.

The comparison, and the number each side uses

1. Compute the conductor ampacity from its own column, with ambient correction and conductor count adjustment applied.
2. Read the termination limit from the column set by 110.14(C), with no correction and no adjustment applied to it.
3. The usable figure is the smaller of the two.
4. If the conductor is 14, 12 or 10 AWG, check the small conductor cap in 240.4(D) against the overcurrent device.

Step two is where the marks are lost. Applying the derating factors to the termination column produces a smaller number than the code asks for, which oversizes the conductor and reads as a safe error. It is still wrong, and an item with four plausible sizes in the options will have that answer sitting in it waiting.

The reverse mistake is worse. Carrying the derated 90 degree figure straight to the terminations skips the check entirely and undersizes the conductor against equipment that cannot take the heat.

What this looks like on a job

A conductor that pencils out fine and fails inspection usually failed here. The installer sized from the 90 degree column because the wire was THHN, and the gear was 75 degree gear.

The useful field version of the rule is short. Buying a higher temperature insulation does not raise the termination limit on the same size of wire, because the limit is read off a column the insulation rating does not enter. Going up a wire size does raise it, because a larger conductor has a larger ampacity in that column too.

Which is why the fix on a marginal run is a bigger conductor or different equipment, and never a different letter on the jacket.

What this page cites

• NEC 110.14(C) Temperature limitations. The opening sentence coordinates the ampacity to the lowest rated part of the path and permits a higher rated conductor to be used for ampacity adjustment, correction or both. (C)(1) carries the equipment provisions, split at 100 amperes and at 1 AWG, with the motor design letter option and the listed and identified escape. (C)(2) carries separately installed pressure connectors. Not revised in the A2025 cycle that produced the 2026 edition: absent from both Code-Making Panel 1 draft reports, which do revise 110.14 generally and 110.14(D). source
• NEC Table 310.16 The ampacity table the termination provisions are determined from, and the source of both the 60 degree and 75 degree columns this section sends you to.
• NEC 310.15 Correction and adjustment. These apply to the conductor ampacity at its own temperature rating and do not apply to the termination column.
• NEC 240.4(D) Small conductors. A separate cap on the overcurrent device for 14, 12 and 10 AWG, applied after correction and adjustment.