Services and feeders · copper or aluminum · NEC 2023
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Worked example — for a 200 A dwelling service, copper, 30 °C ambient, three current-carrying conductors, the engine returns:
2/0 CU — OCPD 200 A · GEC 4 · EGC 6
How it works. Sizing a service or feeder conductor starts from the calculated demand, then applies the ampacity corrections that actually apply to the install — ambient temperature and how many current-carrying conductors share the raceway. The result is then checked against the overcurrent device and the grounding conductor tables, which follow their own rules.
What this covers: 75 °C column only. Correct for the 100–400 A dwelling service/feeder range (110.14(C)(2)); optimistic for ≤100 A equipment, which 110.14(C)(1) puts on the 60 °C column.
Educational reference, not code. Based on NEC (NFPA 70) 2023 (310.16 · 240.4 · 250.66). Your state or local AHJ may enforce a different edition or amend it — theirs is the one that counts. No NEC text is reproduced here.