Power lines

Power lines are made of two materials, copper and an aluminum wire with a steel core. Transmission lines (also all new construction) are usually made of the aluminum variety. This is because while copper is a better conductor, and is stronger, copper is also very expensive and Heavy. In contrast, aluminum is also quite conductive, very light, and not to mention cheap in comparison. One downside to aluminum is it’s quite a lot weaker than copper, which is where the steel core comes in. The combination of aluminum (good conductor, cheap, weak) and steel (only okay conductor, cheap, and strong as heck) make both a cost effective and strong material to make new lines with.

Also worth noting, a big problem in the power line industry is copper theft. Not only is it dangerous to the thief, but those wires are essential to the safety of the utility workers and reliability of the grid. **

** I never understood why people steal copper, they don’t realize how dangerous it really is. In my area alone there has been 3 deaths of thieves in the past 10 years. With the price of copper and the time it takes, you'd make more sweeping the parking lot for some generous small business, a lot safer too.