Why is bare copper electrical wire not suitable for aircraft use?

• A. It is too expensive
• B. It oxidizes rapidly
• C. It is too brittle
• D. It has too high resistance

Answer: (B)

Bare copper is not suitable because it oxidizes quickly when exposed to air and moisture, forming an insulating oxide layer that raises resistance and can cause poor or intermittent electrical connections. In aircraft, wiring must stay conductive and reliable under vibration, temperature extremes, and exposure to humidity and contaminants, so conductors are insulated and often tin-coated to resist oxidation and provide mechanical protection. The other issues listed aren’t correct: copper isn’t particularly expensive, it isn’t brittle (it remains ductile), and it has very low resistance, not high.