NEC-Electrician: Conductor Ampacity Basics - Wire Size vs Current — Flashcards

Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. Ampacity depends on conductor size (AWG/kcmil), insulation temperature rating (60°C, 75°C, 90°C), ambient temperature, and number of current-carrying conductors per NEC tables (e.g., Table 310.16).

Worked example:
A #12 AWG copper THHN (90°C) conductor is typically rated 30A in the 90°C column, but if termination is rated 60°C, allowable ampacity is limited to 20A (per 60°C column for #12).