Overhead power transmission lines have voltages ranging from less than 1000V (for connections within residential areas) to over 800,000V (for long distance/very high power transmission)! These voltages are strong enough to kill a giant elephant if the power line falls on the elephant on the ground. Have you seen birds perching on these live power lines comfortably without being electrocuted? Have you ever asked yourself why those birds are not electrocuted?
For electricity to kill any animal through electrocution, electric current must flow through the animal. For electric current to flow from one end to another end, there must be a complete circuit (a closed circuit) as well as potential difference ( electrical pressure difference) between the two ends.
Now, for a bird sitting on the live power line, the circuit through the bird is incomplete as the bird is not in contact with any other wire or any other object touching the ground. If any other part of the bird touches another wire or any other object on the ground while still sitting on the power line, the circuit through the bird will be completed and the bird will be roasted! Again, the two feet of the bird are resting on the same live wire. So, the two feet are at the same potential. If one foot of the bird is on live wire and the other foot is on the earth wire, then, there would be a complete circuit through the bird and the bird will be roasted alive!
This is why it is very dangerous to fly a kite till the kite touches overhead power line. When this happens, there will be current flow from the wire through the kite through the person involved into the ground! Fatal! There is a complete circuit here. A teenager flying kite in Yorkshire once died through this!
It is not the electrical potential that kills an animal during electrocution but the voltage difference. It is the voltage difference the brings about current flow that does the damage (Ohm’s Law). Another important factor that keeps the bird alive while still sitting on the live wire is the fact that current flows through the path of least resistance. The power line is a metallic conductor with negligible resistance when compared to that of the bird. So, the current keeps flowing through the wire without branching into the bird.
One of the lessons we can learn here is that when we are working with electricity or live wire, we should put on strong rubber/plastic shoes. Rubber/plastic is an insulator. If by accident, we touch the live wire, the circuit through our body into the ground will not be completed. The circuit will be broken by the rubber/plastic shoes. As such, there won’t be current flow and we won’t be electrocuted.
Watch the animation video below:
(Photo Credit: www.alamy.com, www.colourbox.com, Video Credit: www.atcoelectric.com)
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