Electrical Cable Size Link

[ VD = 2 \times K \times I \times L / A ]

[ R = \rho \fracLA ]

Always consult the latest edition of your local electrical code (NEC, CEC, IEC, BS 7671) as legal requirements supersede engineering approximations. Last reviewed: April 2026. This guide is for informational purposes. Always involve a licensed electrical engineer for critical installations. electrical cable size

#2 AWG: 1.54 ohms/1000 ft → R = 0.46 ohms → VD = 9.2V (7.7%) – getting close.

#6 AWG: 2.4 ohms/1000 ft → R = 0.72 ohms → VD = 14.4V (12%) – still high. [ VD = 2 \times K \times I

Conclusion: For long runs, voltage drop (not ampacity) dictates cable size. Here, 150 ft at 20A needs 1/0 AWG copper despite #12 AWG being fine for 20A at short distances. For feeders and services, ensure cable can survive fault current. Most NEC installations skip this for small branch circuits because upstream breakers trip quickly, but for large feeders (e.g., 1000A service with 50kA fault current), verify using adiabatic equation.

Example: 90°C wire in 50°C ambient → factor 0.71. NEC 310.15(C)(1): More than 3 current-carrying conductors in a raceway or cable. Always involve a licensed electrical engineer for critical

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.