What is the acceptable conductor material specified in the NEC if not otherwise indicated?

The National Electrical Code (NEC) primarily specifies copper as the acceptable conductor material unless stated otherwise. Copper is preferred due to its excellent conductivity, which contributes to reducing energy losses in electrical installations. It also has good mechanical strength and resistance to corrosion, making it a durable choice for a wide range of applications.

When wiring systems are designed, copper conductors are the default choice for residential, commercial, and industrial installations since they offer a combination of reliability and efficiency. While aluminum is also used in certain circumstances—especially for larger conductors due to its lighter weight and cost-effectiveness—copper remains the standard unless an alternative is specifically indicated. This emphasizes the importance of understanding the material properties and applications when following NEC guidelines.