[ R = \rho \fracLA ]
#10 AWG: 3.9 ohms/1000 ft → R = 2×150/1000×3.9 = 1.17 ohms → VD = 23.4V (19.5%) still too high.
Introduction Selecting the correct electrical cable size is one of the most critical decisions in any electrical installation—whether it’s a low-voltage automotive circuit, a residential feeder, or a high-voltage industrial distribution network. An undersized cable overheats, destroys insulation, causes fires, and creates excessive voltage drop. An oversized cable wastes material, increases cost, adds unnecessary weight, and may be difficult to terminate.
[ VD = 2 \times K \times I \times L / A ]
Example: 50A load, 75°C terminals, 3 conductors in conduit, ambient 30°C. Table says #8 AWG (50A at 75°C) is borderline; #6 AWG (65A) provides margin. Never use raw table values directly. Apply all that apply: 3.1 Ambient Temperature Correction (NEC Table 310.15(B)(2)(a)) If ambient ≠ 30°C (86°F), multiply ampacity by factor.
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