Wire Size for Voltage Drop

Worked example — for 20 A, 150 ft one way, 240 V single-phase copper, 3.0 % recommendation, the engine returns:
8 AWG minimum — 1.95% drop (4.7 V), within the 3.0% limit

How it works. This works backwards from the usual question. Instead of checking a size you already picked, it takes the load, the distance and the drop you can afford, and returns the smallest conductor that stays inside that limit. Useful when a run is long enough that voltage drop, not ampacity, is what actually decides the size.

What this covers: Answers voltage drop ONLY. The conductor must still satisfy ampacity — check it in Wire & Service Sizing.

Educational reference, not code. Based on NEC (NFPA 70) 2023 (Ch. 9 · Table 8). 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.