Final answer:
Wire connectors marked with wire size should be used with copper conductors, as aluminum requires different connectors due to its higher thermal expansion and oxidation issues, which can lead to electrical failures.
Step-by-step explanation:
Wire connectors marked only with the wire size should be used only on copper conductors. This is because aluminum conductors require different considerations due to their material properties.
Aluminum has a higher rate of thermal expansion than copper, and also has a tendency to oxidize, which does not conduct electricity and can lead to connection failures.
Therefore, special connectors and techniques are needed for aluminum wires to prevent loose connections and possible fire hazards.
It's important to note that the American Wire Gauge (AWG) standard is used to categorize wire sizes, with higher gauge numbers indicating thinner wires. Proper understanding of wire gauge and the corresponding current-carrying capacity is crucial in electrical applications to ensure safety and functionality.