When the NEC refers to the term conductor without specifying the material, which material does it default to?

The National Electrical Code (NEC) defaults to copper or aluminum when referring to the term conductor without specifying the material. This is because copper and aluminum are the two most commonly used materials for electrical conductors in residential and commercial wiring.

Copper is preferred for its excellent conductivity and durability, while aluminum is often selected for its lightweight and cost-effectiveness, especially in larger wiring applications such as power distribution. By stating that the term "conductor" defaults to copper or aluminum, it provides clarity and coverage for a wide range of electrical installations, acknowledging that different applications may call for different materials based on various factors like cost, weight, and conductivity.

The other choices can be interpreted as more restrictive. For instance, specifying just aluminum or copper would not account for the combined use of both materials in various scenarios. The mention of "insulated" in the options does not pertain to the material of the conductor itself; rather, it refers to the type of conductor applicable to specific applications, thus making it a less relevant choice.