3.1 Conductor Ampacity & Bundling Derating
Apply Table 310.16 ampacities, temperature correction factors, and Table 310.15(C)(1) adjustment factors for more than 3 current-carrying conductors.
Key Blueprint Takeaways
- 4 to 6 current-carrying conductors in a raceway require an 80% derating factor.
- 7 to 9 conductors require a 70% factor; 10 to 20 conductors require a 50% factor.
- Continuous loads require conductors to be sized at 125% before applying derating factors.
Conductor ampacity is the maximum current in amperes a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
When multiple conductors are packed into a single raceway, mutual heating reduces allowable ampacity. Table 310.15(C)(1) mandates derating percentages to ensure heat safely dissipates into the surrounding environment.
Knowledge Checkpoint • Section 3.1
When installing more than three current-carrying conductors in a raceway, what adjustment factor does NEC Table 310.15(C)(1) require for 4 to 6 current-carrying conductors?