Base tables assume 30°C ambient. Attics + rooftop conduit can hit 50–60°C in summer.
Conductors in raceway
Count each current-carrying conductor. Neutral in a 3-wire single-phase or 4-wire 3-phase serving nonlinear loads (LED, VFD, etc.) counts. Ground does not.
Derated ampacity
— A
from — A base
⚡ Teaching + field-reference tool. Uses NEC 310.16 base ampacities + Table 310.15(B)(1) temperature correction + Table 310.15(C)(1) adjustment factors. CEC Section 4 (Table 2, 5A, 5C) produces similar results with slightly different numbers. Real installations require checking terminal temperature rating (usually 75°C for 100 A+ per NEC 110.14(C)/CEC 4-006) — the FINAL allowed ampacity is the LOWER of derated conductor ampacity and terminal-rated ampacity. Always follow the tables in your adopted code edition.