What is the minimum conductor size for copper and for aluminum or copper-clad aluminum?

• A. 8 AWG copper and 6 AWG aluminum or copper-clad aluminum
• B. 6 AWG copper and 8 AWG aluminum
• C. 4 AWG copper and 2 AWG aluminum
• D. 10 AWG copper and 8 AWG aluminum

Answer: (A)

The main idea is that aluminum conducts, and thus safely carries, less current than copper for the same cross‑section, so it must be larger to achieve the same ampacity. Copper is more conductive, so a smaller gauge can carry the needed current; aluminum (and copper-clad aluminum) needs a larger cross-section to reach the same capacity. That’s why the minimums are a copper size of 8 AWG and an aluminum or copper-clad aluminum size of 6 AWG. Copper-clad aluminum is treated like aluminum for ampacity, since its conductivity is dominated by the aluminum content. In short, to carry the same current safely, you use 8 AWG copper or 6 AWG aluminum (or copper-clad aluminum).