You've hit upon a very common point of confusion! The NEC doesn't explicitly tell you to use the 60°C or 75°C column for conductors based on the ampacity you're calculating. Instead, it depends on the termination temperature rating of the equipment you are connecting to. Here's the breakdown and how it applies to motor circuits

Understanding Termination Temperature Ratings (NEC 110.14(C))
What it is

Electrical equipment (like breakers, contactors, starters, and the motor itself) has a temperature rating for the terminals where you connect the wires. This rating specifies the maximum temperature the terminal can safely handle.

Why it matters

If you connect a conductor with an ampacity rating higher than the terminal's temperature rating allows, the terminal can overheat, causing a fire hazard.

The Rule (Simplified)



You must select a conductor ampacity based on the lowest temperature rating of any termination point in the circuit. This ensures no termination overheats.

How This Applies to Motor Circuits1. Motor Terminals

Most motors are marked to indicate the conductor temperature that must be used. If not marked 110.14(C)(1) B 1 states "Equipment marked for use with 60°C or 75°C conductors shall be permitted to be terminated with 75°C conductors where the ampacity of the conductors does not exceed the 60°C ampacity". If the motor states 75 degree then you can use the 75 degree column.
2.

Overcurrent Protection (Breakers/Fuses)



Generally, breakers and fuses are rated for 75°C. This is a common assumption, but always verify the markings on the specific device.3. Other Devices (Starters, Contactors, Disconnects)

Check the markings on these devices as well. They may be rated for 60°C or 75°C.

The "100 Amp Rule" - A Common Misconception

The idea that you use the 60°C column for under 100 amps and 75°C for over 100 amps comes from NEC 110.14(C)(1)(a) for terminals. This section applies to conductors No. 14 AWG through 1 AWG. For equipment rated 100 amps or less, you must use the 60°C column ampacity for those smaller conductors, unless the equipment is specifically marked and listed for use with conductors rated 75°C.

Key Takeaways for Motor Circuits Always Check Markings

Never assume the temperature rating of any piece of equipment. Check the nameplate, the device itself, or the manufacturer's documentation.

Use the Lowest Rating

Find the lowest temperature rating of any terminal in the motor circuit (motor terminals, breaker, starter, etc.). Use the corresponding ampacity column in the NEC tables (Table 310.16, etc.).

Motor FLC Calculation is Separate

The motor's Full Load Current (FLC) from Tables 430.247-430.250 is used before you consider conductor temperature rating. You're calculating the minimum required ampacity of the conductor (FLC x 1.25 for continuous duty), and then selecting a conductor size that meets that ampacity requirement while also respecting the termination temperature limitations.



Don't Forget Adjustments

After determining the conductor size based on temperature ratings, remember to apply any required ampacity adjustment or correction factors (for ambient temperature, number of conductors in a raceway, etc.).

Example Scenario1.

Motor

5 HP, 230V, single-phase motor. FLC from Table 430.248 is 28 amps. The motor nameplate is marked 75°C terminals.
2.

Conductor Ampacity Required

28 amps x 1.25 = 35 amps (continuous duty).
3.

Breaker

Assume the breaker is rated for 75°C terminals.4.

Lowest Rating

In this case, both the motor and breaker terminals are rated 75°C.5.

Conductor Selection

Using the 75°C column of Table 310.16, a #8 AWG copper conductor is rated for 50 amps, which is greater than the required 35 amps. So, a #8 AWG copper conductor would be sufficient before any adjustment or correction factors.

In SummaryForget the "under/over 100 amp" rule when dealing with the motor itself. Focus on finding the lowest termination temperature rating in the entire circuit. Use that rating to choose the appropriate ampacity column in the conductor ampacity tables. Remember to ALWAYS VERIFY the terminal ratings of all the equipment in the circuit. Good luck with your exam! Flag for review