Why Doesn’t a Bird on a Power Line Get a Shock?

The Answer

Both of its feet are on the same wire, at the same voltage. With no difference in voltage across its body, there's nothing to push a current through it.

Electric current flows from a point at a higher voltage to one at a lower voltage, a bit like water flowing downhill. Voltage on its own does nothing; it's the difference between two points that drives a current. The bird's feet are a few centimetres apart on the same thick metal wire, so they're at almost exactly the same voltage. The bird sits at 11,000 volts with almost no current flowing through it at all.

Danger comes when something touches two points at different voltages at once. A person on a ladder who touches a line is connected to the wire through one hand and to the ground through their feet, and the ground is at zero volts. Thousands of volts then drive a current through their body. Large birds such as eagles and storks are sometimes killed when their wings touch two wires, or a wire and the pole, at the same time. Power companies fit insulating covers and safe perches on poles where big birds live.

Line workers use the same idea. Some work on live high-voltage cables from helicopters, wearing suits woven with metal. They first connect themselves to the cable so that they're at its voltage, and then they can touch it safely.

The principle: Potential difference. A current only flows through something when there's a voltage difference across it; touching a single wire gives no difference, but touching a wire and the ground does.