Electricity and Air: A Fascinating Interaction

[phymathlover]

A bird perches on a bare high power line and nothing happens to it. A man standing on the ground touches the same line and gets a fatal shock. This is supposed to be because there is potential difference between the ground and the line which the man touches but similarly, isn't there also a potential difference between the line and the air to which the bird is exposed and thus a potential difference and so shouldn't the bird also get a shock? I know that air is an insulator but since the high transmission lines have large electric fields around them so this should cause breakdown of air?

 

[SteamKing]

The breakdown voltage for air is much larger than the line voltage. The field strength for the breakdown of air is greater than 3 MV/m. If electric transmission lines grounded with the air, it would be impossible to transmit electricity in this fashion without zapping everything near the lines.

 

[UltrafastPED]

Also note that you, as a person, are not a great insulator ... and being the path of least resistance is from the line voltage thru you to the ground.

If a bird is big enough to touch two wires simultaneously you will get roast buzzard!