Wood and fiberglass cross arms have an electrical advantage because of their ?.

• A. Decay resistance
• B. High conductivity
• C. Insulating properties
• D. Superior strength

Answer: (C)

The key idea is that cross arms on power lines are meant to keep conductors isolated from the pole and from each other. Wood and fiberglass provide an electrical disadvantage to current flow because they act as insulators. They have high electrical resistance and good dielectric strength, so they don’t conduct electricity readily or allow arcing to the structure or to neighboring conductors. That insulating behavior keeps the live parts safely separated and reduces leakage currents.

Other properties like decay resistance or strength matter for durability, but they don’t give the line its electrical protection. High conductivity would be dangerous because it would allow current to travel through the arm itself.