Cable Ampacity Vs Conductor size

Many cable consultants have approached me for advice on conductor sizing, and one of the most common questions they ask is whether doubling the conductor size will double the cable's ampacity. The simple answer is not necessarily. While increasing the conductor size does enhance ampacity, the relationship between conductor size and ampacity is not linear due to various influencing factors. In most cases, doubling the conductor size increases the cable's ampacity by only about 40%, rather than a full 100%.

This is because, while a larger conductor reduces electrical resistance and minimizes heat generation, the increase in ampacity is constrained by heat dissipation, insulation properties, and installation conditions. In AC systems, the skin effect further limits the effective current-carrying capacity of larger conductors at higher frequencies. As a result, even though a thicker conductor can handle more current, its actual ampacity gain is not directly proportional to its size.

Industry standards, such as those from IEC and NEC, provide ampacity tables that reflect these practical limitations. They show that while a larger conductor does carry more current, the increase is always less than twofold when the cross-sectional area is doubled. Therefore, selecting the right conductor size requires careful evaluation of not only ampacity but also thermal management, installation constraints, and economic considerations to ensure optimal performance and efficiency.