You're on the right track in understanding 110.14(C). Let's break it down

Understanding 110.14(C): Temperature Limitations

This section ensures that the heat generated by a conductor doesn't damage terminations, connected equipment, or the conductor itself. It's a critical safety requirement. Lowest Temperature Rating Governs

The key is the "lowest temperature rating." You need to identify the temperature ratings of all components in the circuit:

Conductor

The insulation rating (e.g., THHN, XHHW). This is usually 90°C.

Terminations

The terminals where the conductor connects (e.g., circuit breakers, switches, receptacles, equipment lugs). These are often rated for 60°C or 75°C. You need to check the equipment's labeling or instructions. Many newer devices are now rated for 75°C, but you absolutely must verify.

Devices

The equipment the circuit serves. The equipment will be designed to accept a certain current and corresponding heat generated, usually 75 degrees C or greater.

The Constraint

The final ampacity you use for your conductor (after any derating) cannot result in a temperature at the termination exceeding its rating. If you are connecting to equipment listed and marked for use with 75 degree C conductors, you may use the 75 degree C ampacity of the conductor selected.

Your Example Scenario

Let's refine your understanding in the context of your described scenario. Imagine that you have terminations at a 75°C breaker.1.

Start with Table 310.16

You look up the initial ampacity of your conductor based on your calculated load.2.

Derating

You apply any necessary derating factors for ambient temperature and the number of current-carrying conductors.3.

110.14(C) Check

After derating, compare the adjusted ampacity with the ampacity of the conductor in Table 310.16 at

the termination rating (in your example, 75°C). The adjusted ampacity must not exceed the 75°C value in the table even if the conductor insulation is rated higher (e.g., 90°C).

Addressing Your Specific Question "Is 110.14(c) saying your final adjusted ampacity can not exceed the 60°C or 75°C ampacity in table 310.16?" YES, assuming your terminations (breakers, equipment, etc.) are only rated for 60°C or 75°C. If the lowest temperature rating of any connection point in your circuit is 75°C, then your final adjusted ampacity cannot exceed the 75°C ampacity listed in Table 310.16 for that conductor size. If the lowest temperature rating of any connection point in your circuit is 60°C, then your final adjusted ampacity cannot exceed the 60°C ampacity listed in Table 310.16 for that conductor size.

Oversizing and the Exception in 110.14(C)

The second sentence of 110.14(C) is crucial: "Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both."

This allows you to use a 90°C-rated conductor for calculating your ampacity adjustments and corrections (derating). However, the final adjusted ampacity still cannot exceed the ampacity listed in Table 310.16 for the termination's temperature rating (60°C or 75°C).

Example

Let's say you need an ampacity of 50 amps after derating. Your terminations are rated for 75°C. You use THHN (90°C rated) wire.1. You can use the 90°C column in Table 310.16 to perform your derating calculations. A smaller THHN conductor may be able to be used based on the 90 degree rating to compensate for the derating factors.
2. After derating, the resulting ampacity of the conductor must not exceed the ampacity in the 75°C column of Table 310.16 for that conductor size.

In summary:1. Determine the termination temperature rating of all connections. This is usually 60°C or 75°C, but always check the equipment labeling.
2. Select a conductor with an insulation rating of 90°C.3. Do your ampacity adjustments and corrections calculations with the 90°C rating.
4. Make sure the resulting ampacity of your conductor does not exceed the ampacity rating of that conductor in the 60°C or 75°C column of Table 310.16, depending on your termination temperature rating.This process ensures that you're operating within safe temperature limits at the terminations, preventing potential overheating and failures. Flag for review