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Name: Karl H.
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A


Question:
How does the string of a kite allow electricity to flow through it to ground, upon hitting power lines? I assumed string is a bad conductor, or is it not string?



Replies:
Assuming the power line is not insulated, the kite string can act as a conductor because it almost certainly is damp. Then of course any water will dissolves electrolytes, making it a reasonably good conductor. So while dry string is a relatively poor conductor, wet (or even damp) string has a much higher electrical conductivity.

Vince Calder


Some kite strings have a metal core which transmits electricity rather well. Even the regular type will transmit electricity if it hits a high voltage line. The voltage over powers the resistance so that enough current flows to do a very fine job of eliminating anyone holding the string.

R. W. "Bob" Avakian
Oklahoma State Univ. Inst. of Technology


Hi there Karl,

Kite string, whether it is jute or nylon or cotton, is a RELATIVELY poor conductor of electricity. In fact if you are only dealing with 12 volts, as in a car, then any of those would be a good insulator.

When you fly a kite however, there are at least three factors working to increase you danger from power lines.

First, power lines are NEVER at twelve volts. In most countries (not the USA) domestic power lines, the ones that might run up your street, are at least 240 Volts - more than enough to kill you. In the USA domestic power is at 120 Volts. If your power lines run to a substation, they might be carrying 720, or even 7,200 Volts or much higher. If they are the overland type of power lines on huge pylons, they can be carrying anything up to 672,000 Volts. As you consider more and more volts, materials like cotton and nylon become less and less useful as insulators. Unless they are several inches thick they cannot stop the electricity from sparking through them.

Second problem with kite strings - you use them outside, where the string can absorb moisture. Natural fibres, such as jute and cotton are particularly good at absorbing moisture even on a relatively dry day. Woven nylon string will become very damp on a day where there are any signs of moisture in the air, such as mist, or drizzle. Once the string is damp, the water does not just reduce the insulating properties of the material, it actually turns the string into a conductor, and provides a path for the electricity straight from the power lines to you - because you are holding the other end. Since the electricity wants to get to the ground, and you are keeping the string off the ground, the electricity will travel through you.

Factor three is the fact that power lines always carry alternating current. While a huge DC current can cause extensive burning and damage to flesh and tissue, and AC current is rapidly switching on and off. Even at domestic voltages (120 and 240V,) an AC Current can interfere with the signals that control your heart rate and can cause your heart to stop.

So, three reasons why kite strings and power lines are a BAD combination. Definitely NOT worth the risk!

Happy kite flying, but stay away from power lines!

Nigel Skelton
Tennant Creek High School
AUSTRALIA



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