Power Line Sag

I was watching Nova ScienceNOW and heard something interesting. This quote is from “More Power To the Grid” in the Oak Ridge National Laboratory Review:

One major transmission problem has been power-line sag. When hot weather generates demand for more electricity for air conditioning, power lines heat up, stretch, and sag. If an overloaded line sags into a tree, the current can be discharged to the ground, causing a short circuit and sometimes triggering a major power outage. Sag was a cause of the two major U.S. blackouts in 1996 and 2003.

(The article is about a new power line from 3M which will not sag as much.)

I know energy had an affect on materials. It just had not occurred to me more electrons in a wire stretched them like this. This is the kind of thing which would make a physics class cool.

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