aTypical Joe: a gay New Yorker living in the rural South

Thursday, July 28, 2005

Why can birds sit on power lines?

Four adult Boy Scout leaders were electrocuted on Monday. Power lines on poles are not insulated:

Most of the hundreds of thousands of miles of high-voltage transmission lines in this country are made solely of metal-either aluminum or aluminum wrapped around a steel core. Adding a layer of insulation to every line would be pricey and has been deemed unnecessary given how high the lines are off the ground.

So what about birds?

Electricity will stray from a power line only if it has a direct path to the ground. If you hang from a power line with both feet in the air, you won’t get shocked-that’s why birds can sit on a line with no insulation. (Birds do get zapped when they touch two lines at the same time or one line and the grounded wooden pole that supports it; power companies try to prevent bird deaths by increasing the space between the wires.)

Just stay away:

The air around a power line isn’t a good conductor, but very high voltages do create a significant electrical field. For large-scale transmission lines, this field can have a radius of a foot or more. That means electricity could arc out of the wire to any crane or pole that gets close enough, even if it never makes contact.

Most power companies warn workers to stay 10 feet away from power lines and up to 25 feet away from the highest-voltage lines. Even regular folks trimming trees near a power line need to take care-wood isn’t as conductive as metal, but a stray branch can still transmit a deadly shock down the trunk.