Sizes (or checks) a copper or aluminum conductor against NEC Article 310, applying all four steps of the standard derating chain: the base allowable ampacity from Table 310.16 at the conductor's insulation temperature rating, the ambient-temperature correction factor from Table 310.15(B)(1), the bundling/adjustment factor from Table 310.15(C)(1) for more than 3 current-carrying conductors, and finally the 110.14(C) termination-temperature cap — the usable ampacity can never exceed the Table 310.16 value for the termination's own (often lower) temperature rating.
Standards followed
NEC Table 310.16 — allowable ampacities of insulated conductors, 30°C ambient, ≤3 current-carrying conductorsNEC Table 310.15(B)(1) — ambient temperature correction factorsNEC Table 310.15(C)(1) — adjustment factors for more than 3 current-carrying conductorsNEC 110.14(C) — conductor temperature limitation at terminations
What it can do
- Auto-size mode: finds the smallest AWG/kcmil conductor whose derated, termination-capped ampacity meets the load.
- Check mode: evaluates a specific conductor size you already have in mind and reports pass/fail with full derating breakdown.
- Copper or aluminum, 60/75/90°C insulation ratings, 60/75°C termination ratings.
Example problem
65A load, 75°C insulation and termination, copper, 30°C ambient, 3 current-carrying conductors.
- At 30°C/≤3 conductors, ambient factor = 1.00 and bundling factor = 1.00 (no derating needed).
- #6 AWG Cu at 75°C = 65A base ampacity — exactly meets the 65A load once the termination cap (also 65A at 75°C) is checked.
#6 AWG copper, 75°C — 65A effective ampacity, meeting the 65A load exactly.
Table 310.16 figures are the standard published NEC values, unchanged across the 2014–2023 NEC editions for this table — but always confirm against the specific code edition adopted by the AHJ, and remember this is ampacity only: voltage drop, short-circuit withstand, and conduit fill must be checked separately (see the Cable Sizing, Conduit Fill, and Feeder Tap Rule calculators).