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Voltage drop = 2 × resistance per foot × length × current (for single-phase). NEC recommends maximum 3% drop for branch circuits, 5% combined for feeder+branch. Resistance = 2 × 12.9 / (1000 × conductor area in circular mils) for copper. Wire gauge (AWG) inversely relates to size: #12 AWG = 6,530 CM; #10 = 10,380 CM. Excessive voltage drop causes equipment malfunction and heat buildup.
Copper single-phase: Vd ≈ 2×K×I×L/CMIL (K≈12.9).
~3.95 V