The American approach: imperial units (AWG, feet), DC resistance from Chapter 9 Table 8 (or Table 9 impedance for large AC), and the famous 3%/5% figures that are recommendations in the base code — and requirements everywhere energy codes, fire pumps, or project specs say so.
Vd = 2 × I × L × R / 1000 single-phase (√3 three-phase), with R in Ω per 1000 ft at 75 °C from Chapter 9 Table 8; conductors above ~4/0 on AC use Table 9 impedance instead. The field shortcut is the K-factor (12.9 copper / 21.2 aluminum). Limits: ≤3% branch (210.19(A) Informational Note No. 4) and ≤5% feeder + branch combined (215.2(A) IN No. 2) — full enforceability discussion on the limits page.
The 3%/5% recommendation itself hasn't changed in decades; what moves between editions is numbering and the rules around it:
Voltage-drop notes unchanged. The notable adjacent change: 110.14(D) made torque-tool verification of terminations a requirement — directly relevant to aluminum feeders and parallel sets. IECC energy-code adoptions increasingly bind the 2%/3% drop limits in commercial work.
The everyday ampacity table was renumbered from 310.15(B)(16) to Table 310.16 (the numbering this site uses). Substance of the drop notes unchanged; GFCI and surge-protection expansions dominate the edition.
Article reorganizations shuffle some informational-note numbering, but the 3% branch / 5% total guidance is intact. Fire pump limits (695.7 — 15% starting / 5% running) remain hard requirements. Always confirm which edition your jurisdiction has adopted — many run one or two cycles behind.
Data follows NEC 2023 numbering (Table 310.16, Chapter 9 Table 8); the underlying resistance and ampacity values are stable across recent editions, so results apply under 2017 and 2020 adoptions too.
Widely — much of Latin America, the Middle East and the Philippines adopt the NEC or derivatives. If your spec cites NFPA 70, this method applies regardless of geography.