Why don’t birds on power lines get electrocuted?

By Matthew Allen

Have you ever wondered why birds sitting on power lines don’t get electrocuted? We’re always told as children to stay away from electric wires and plug sockets (and rightfully so!), but how are birds able to sit on electricity wires without getting a shock?

Electricity can be very dangerous. An electric shock which reaches a human’s heart for just a few seconds is enough to interrupt the natural rhythm of the heart, causing serious problems to the other organs of the body; this is why we’re told not to put our fingers in plug sockets, not to stick a knife in a toaster and certainly not to touch the power cables above our heads, which carry electricity to our homes. But, if these power cables are so dangerous, how come birds are able to sit on them without getting an electric shock? It’s all down to how electricity travels through things.

Electricity is Lazy

Birds lining up on a power line

Why are these birds sat on the power cable not getting electrocuted?

The way to remember how electricity travels from one point to another (such as along a wire), is that electricity is incredibly lazy – it will always take the easiest route!
In physics we say that electricity (or current) travels from the point of highest potential to lowest potential. You can think of how electricity travels through an object as dropping a ball on the side of a mountain. The ball is like the current, it will always fall down the mountain. The ball will never fall up the mountain. In a wire, one end of the wire is at a different potential than the other, so the electricity wants to travel along it. As both of the bird’s feet are on the same wire, there is no difference in potential between them (imagine the bird as a flat part of the mountain, where the ball will neither fall up or down the mountain). The electricity will prefer to continue travelling along the wire, rather than passing through the bird.

Imagine if you had to walk to your local shop to buy a loaf of bread. You can walk one of two possible routes: along a nice flat footpath or through a muddy, boggy, waist deep swamp. You’d probably choose the footpath, because it’s much easier to walk along it. This is what electricity does, it travels along the easiest path, which we call the path of least resistance. Engineers specifically design wires so that it is very easy for electricity to travel down them. Our bodies and birds bodies on the other hand offer a lot of resistance to the electricity travelling down them. The electricity therefore will preferentially continue travelling down the wire, as it’s an easier route for it to take, rather than passing through the bird.

It is these reasons why our feathered friends can happily sit on power lines without getting shocked!

…but

A power cable repairer using a helicopter to safely repair the cable

Power cable repairers often access the cables using a helicopter, hovering above. Because the helicopter isn’t touching the ground, electricity doesn’t flow through the repair person.

What if we wanted to give the birds a zap of electricity? What if we were some cruel superhero who wanted to electroute all birds – what could we do to make them get an electric shock from sitting on the wire? Well, we could make a big difference in potential between the bird and the wire. There are two easy ways of doing this. Firstly, we could make the bird touch one of the other power cables running alongside it; power cables typically run at different potentials, so if the bird touched two wires at the same time, then electricity would flow through it. Alternatively, we could make a connection between the bird and the Earth. The earth is at a different potential than the power cable, so electricity would flow from the cable, through the bird and in to the ground, giving the bird a shock! This is why it is very dangerous for humans to touch power cables – if you are somehow connected to the ground when you touch a power cable (maybe you’re stood on a ladder), then you will get a big electric shock!

In conclusion

The reason that birds don’t get electrocuted whilst they sit on power cables is that both the birds feet are at the same potential, so the electricity doesn’t flow through them. Secondly, the bird offers greater resistance to the electricity passing through it than the power cable, so the electricity will travel through the power cable. As long as the birds don’t touch anything else, such as the ground or another power cable, they will continue to sit up there, watching us, trying to spot worms for their breakfast!

Extra science!

Check out these guys below. Notice that whilst they are standing on stools and tables that they aren’t getting shocked, even though they are touching the electric fence. That’s because the stools and tables do not conduct electricity. But, as soon as one of them is touching the ground, the electricity flows from the wire, through 5 people and in to the Earth, causing them all to get a big shock!

About the Blogger – Matthew Allen

Matthew is an astrophysicist who has been working at science made simple since 2016. He has a passion for technology, including Virtual and Augmented reality, statistics and astronomy.


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