# Why don't you get electrocuted when you jump and touch an electric fence?

I've read that you won't get electrocuted if you jump and touch an electric fence because you aren't closing the circuit with the ground. Which is also why birds don't get electrocuted when they're standing on power lines.

The way I understand voltage is that it's basically "a pressure of electrons" in the wire where electrons would like to escape from each other because they are the same charge, and they would love to reach the ground where there is plenty of space (i.e "low pressure"). When you touch an electric fence, the electrons see an opportunity to reach the ground (to "fill the space") through you and you get electrocuted because your body resists the current which makes heat.

Alright, but I don't understand why don't electrons want to fill up your body even you're not touching the ground? Especially at high voltages; I mean there is plenty of space in your body. So when you jump and touch a fence, even though you're not touching the ground, why don't electrons see an opportunity and rush to fill up your body and cause you a shock?

To put it another way, let's say a bird lands on the ground and discharges all the excess electrons (becomes neutral with the ground). Now let's say the bird flies off and lands on a power line. Why don't electrons in the wire rush to fill up the bird and electrocute it?

• In addition to all correct answers, electric fences are often pulsed and don't carry a current continously, but instead only at certain intervals (usually every couple of seconds). When you are jumping across such a fence, it might easily be that you touch the fence when it is off. – ahemmetter Feb 5 '18 at 18:18

Electrons do "fill up your body" when you jump up and hit a high voltage wire - there is a property called the capacitance of the body that determines how much the voltage increases when you add a certain amount of charge - mathematically, $C = \frac{Q}{V}$.
$$C_{sphere} = 4\pi\epsilon_0 R = 0.11 nF$$
At 30 kV, that gives a charge of 3.3 µA; if that charge comes out of your body in 1 µs, it would result in a peak current of 3.3 A which is why it feels like quite a jolt; however, the total amount of energy is only $\frac12 C V^2 = 0.05 J$ - and that is not enough to kill you. It's enough to kill sensitive electronic circuits, which is why you have to be careful how you handle "bare" electronics, especially in winter (low humidity = build up of static electricity as conductivity of air is lower).