Ampacities, NEC 310-15

Ampacities for conductors shall be permitted to be determined by (a) or (b) below. 

(a) General. Ampacities for conductors rated 0 to 2000 volts shall be as specified in the Allowable Ampacity Tables 310-16 through 310-19 and their accompanying notes. Ampacities for solid dielectric insulated conductors rated 2001 through 35,000 volts shall be as specified in Tables 310-67 through 310-86 and their accompanying notes. 

Tables 310-16 through 310-19 are application tables for use in determining conductor sizes on loads calculated in accordance with Article 220. Allowable ampacities result from consideration of one or more of the following: 
1. Temperature compatibility with connected equipment, especially at the connection points.
2. Coordination with circuit and system overcurrent protection.
3. Compliance with the requirements of product listings or certifications. See Section 110-3(b).
4. Preservation of the safety benefits of established industry practices and standardized procedures. 

***Ampacities provided by this section do not take voltage drop into consideration. See Section 210-19(a).