You are incorrect.

Wire can be used for up to whatever ampacity is listed for that size wire and temperature rating in Table 310.16 (Conductor Ampacity) Copper and aluminum have separate ampacity tables because you need to use larger aluminum conductors.

Example:

#250MCM THHN copper can handle 255A in a commercial setting (75C column)

#250MCM THHN aluminum can handle 205A in a commercial setting (75C column).

NEC ampacity table: https://media.distributordatasolutions.com/ThomasAndBetts/v2...