# Hissing high voltage wires. Why? **URL:** \ **Category:** Factual Questions\ **Created:** [May 2, 2008, 12:42am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692 "2008-05-02T00:42:37Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [May 2, 2008, 12:42am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/1 "2008-05-02T00:42:37Z")
I was on a hike under a high voltage transmission line a week ago. I couldn’t help but notice a lot of crackling and popping. Where could this be coming from? Were the wires discharging somewhere? To the air perhaps? It sounded horribly inefficient. Aren’t the wires coated to prevent this? ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [May 2, 2008, 12:44am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/2 "2008-05-02T00:44:42Z")
Corona Noise ---
**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\ **Post date:** [May 2, 2008, 12:55am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/3 "2008-05-02T00:55:03Z")
[QUOTE=solkoe] I was on a hike under a high voltage transmission line a week ago. I couldn’t help but notice a lot of crackling and popping. Where could this be coming from? Were the wires discharging somewhere? To the air perhaps? It sounded horribly inefficient. Aren’t the wires coated to prevent this? [/QUOTE] It’s caused by corona discharge. It’s always present to some degree but can produce audible noise when the field interacts with moisture or air pollutants. At least that’s the way I remember learning it in school. It is inefficient, it creates a line loss, and probably electrical noise as well. The wires are insulated to prevent it, whether it is more prevalent near a bad splice or deteriorating insulation I don’t know. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 2, 2008, 1:01am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/4 "2008-05-02T01:01:06Z")
[QUOTE=HongKongFooey] The wires are insulated to prevent it… [/QUOTE] No, they aren’t. At those voltages, insulators are practically useless at reasonable thicknesses. Effectively insulating such wires would require very thick insulation, adding large amounts of weight, and therefor cost, to the wires and their support structures. In case you’re disinclined to take my word for it, from [Wiki](http://en.wikipedia.org/wiki/Electric_power_transmission): > [@](#): > > Overhead transmission lines are uninsulated wire, so design of these lines requires minimum clearances to be observed to maintain safety. ---
**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\ **Post date:** [May 2, 2008, 1:23am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/5 "2008-05-02T01:23:19Z")
[QUOTE=Q.E.D.] No, they aren’t. At those voltages, insulators are practically useless at reasonable thicknesses. Effectively insulating such wires would require very thick insulation, adding large amounts of weight, and therefor cost, to the wires and their support structures. In case you’re disinclined to take my word for it, from [Wiki](http://en.wikipedia.org/wiki/Electric_power_transmission): [/QUOTE] Point taken. I was thinking of the insulators at the towers or substations [like these](http://www.seeing-corona.com/UGM2004_3.html) We learned to make high voltage splices when I was in school many moons ago and had to learn about the effects of corona discharge. I haven’t had to deal with it much since except in safety courses on arc-flash hazards. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [May 2, 2008, 1:54am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/6 "2008-05-02T01:54:30Z")
In addition to the point made by **Q.E.D.** , insulation reduces the ability of a conductor to liberate heat to the atmosphere, and therefore would result in it being rated at a lower ampacity that that of an equal size bare conductor. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [May 2, 2008, 7:53am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/7 "2008-05-02T07:53:26Z")
What is it about moisture that makes the louder noise? I ask because one of my regular biking routes passes under power lines right next to a lake, and the lines there always seem to be crackling really loudly - much more than other power lines in the area. Does damp air lead to greater losses? ---
**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\ **Post date:** [May 2, 2008, 10:15am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/8 "2008-05-02T10:15:17Z")
[QUOTE=Colophon] What is it about moisture that makes the louder noise? I ask because one of my regular biking routes passes under power lines right next to a lake, and the lines there always seem to be crackling really loudly - much more than other power lines in the area. Does damp air lead to greater losses? [/QUOTE] This is the way I understand it. The air surrounding a bare conductor is acting as an insulator for that conductor. The dielectric strength of air is usually given as 3MV/m, if exceeded it causes ionization of the air molecules. ---
**Author:** ![LouisB](https://avatars.discourse-cdn.com/v4/letter/l/dfb087/32.png) [@LouisB](https://boards.straightdope.com/u/LouisB)\ **Post date:** [May 2, 2008, 10:36am UTC](https://boards.straightdope.com/t/hissing-high-voltage-wires-why/447692/9 "2008-05-02T10:36:23Z")
Our townhouse development happens to be very close to a distribution station and the high voltage lines run adjacent to us. There are days when that crackling noise is very noticeable and days when it isn’t. Even on those days, if you listen closely, you can still hear it. I haven’t noticed any distortion of TV or radio signals; maybe because our TV service is cable and we don’t listen to radio more than once or twice a year. (Think hurricane season.)