Minimum Conductor Size for a Voltage-Drop Target

The smallest standard copper and aluminum conductor that keeps the drop at or below a target percent (default 3%) over the run, from the load current, one-way length, and system voltage, with the resulting drop and an ampacity / termination reminder. The voltage-drop size is a floor, not a substitute for the 310.16 ampacity check.

allowed_drop_V = target% / 100 x source_V; for each standard size smallest-up, drop = (2 for single phase, sqrt(3) for three phase) x K x I x length / cmils with K copper 12.9, aluminum 21.2 ohm-cmil/ft at 75 C; the result is the first size whose drop is at or below the allowed value.

First-principles I x R voltage drop (public); NEC FPN advisory 3% branch / 5% total (informational, not a requirement).

The voltage-drop relation is public physics; the NEC FPN figures are advisory. Free read-only access at nfpa.org/freeaccess.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: phase, material, current_A, length_ft, source_voltage_V, target_percent, min_awg_copper, min_awg_aluminum, resulting_drop_V, resulting_percent

• K-factor model the same model as the voltage-drop tile (copper 12.9, aluminum 21.2 ohm-cmil/ft at 75 C); the search ladder is 14 AWG through 4/0first principles
• Advisory only the NEC FPN 3% branch / 5% total figures are informational, not enforceable; the AHJ governsNEC 210.19 / 215.2 FPN
• Ampacity floor a voltage-drop size is a floor only; verify ampacity (310.16) and the 110.14(C) termination temperature separatelyNEC 310.16 / 110.14(C)