Which of the following is NOT permitted as a conductor material for conductors covered by Article 310?

The correct answer is titanium because it is not listed as an acceptable conductor material in Article 310 of the National Electrical Code (NEC). Article 310 specifically outlines the requirements for conductors, including allowable materials, and focuses predominantly on copper, aluminum, and copper-clad aluminum as suitable options due to their conductive properties and other favorable characteristics in electrical applications.

While aluminum and copper are commonly used because of their excellent conductivity and availability, and copper-clad aluminum is recognized for its cost-effectiveness and performance—titanium does not fall under these accepted materials for general conductor use in this context. Titanium may have specific applications in certain environments due to its corrosion resistance, but it does not meet the standards set forth in Article 310 for general wiring purposes.