Why do power lines sag more in the summer than in the winter?

Sagging Power Lines

In the summer, power lines warm up with the weather. Since materials expand when they get warm, the power lines stretch out and sag. The opposite happens in the winter, as the power lines get colder, they contract. Also, in the summer the electrical load on the line is generally greater. This in turn causes increased temperature and can lead to the line sagging.