Why don't electric workers get electrocuted when only touching one wire? [duplicate]

Question

I know that when electricians work on the poles on the streets, if they only touch one wire at a time they will be fine. However, from my understanding, the negative wire is connected to a large negative terminal, and the positive wire to a large positive terminal. Now for example, if you touch the positive wire, wouldn't all of the electrons get stripped away from your body? Another way to look at it is that current always flows from a higher to a lower potential. If the potential in the wire is 100V (I have no idea what it is) and your potential is 0, wouldn't current flow through you?

Answer 1

AC or DC, you only get electrocuted if current passes through your body. (Current passing through any part of your body can be dangerous, and possibly cause an electrical burn, but current passing across your heart is the one that's really dangerous.) Touching just one wire at a time gives the current nowhere much to go. You are right to think that some electrons can get stripped from your body when you touch a bare wire. But not many. Once they've gone, unless your body gets new electrons from somewhere else, the current stops. If you're standing in a pool of water, or touching a metal pole, or another wire that can conduct lots of electrons from somewhere else, you're fried.

So how many electrons get conducted away from the human if it has no other source of electrons? In this case, the human acts as a capacitor. Now, Wikipedia tells me that one standard for this approximates a human as having capacitance $C=100\,\mathrm{pF}$. This is pretty tiny. (For comparison, the capacitors you might see if you open up a computer or other electronics can easily have capacitance billions of times larger.) If the voltage is $V=100\,000\,\mathrm{V}$ (which is really quite high), the charge that would be transferred is $Q = C\, V = 10^{-5}\,\mathrm{C} \approx 10^{14}$ electrons. You probably have $10\,000$ times more electrons in a single eyelash, so that's not many. The danger there is that at such high voltages, a lot of things become conductive that aren't normally.

P.S. Most electrical wires that you see in a city (though not those for trams, or the really big high-voltage lines) are actually insulated. (I worked as an electrician through college, and have touched many such wires.) So the birds aren't frequently touching anything dangerous to begin with. But even if they were, they'd only be in danger if they had somewhere to get new electrons. There are plenty of places (especially around those big transformers you see) where you can find exposed power, though, so be careful.

Answer 2

When you touch a hydro wire, and ONLY a hydro wire -- nothing else -- there's no potential difference across your body. Your entire body is at the same potential, which is that of the hydro line (often thousands of volts). This is why birds don't get electrocuted if their feet touch only one wire. Plenty of birds, particularly eagles, have been fried because they grabbed onto two wires. Don't touch hydro wires. Especially do not touch hydro wires while simultaneously touching anything else.

Also note, that there is a very slight potential drop across the birds feet, due to ohmic losses of the wire. Since it's a conductor, these are very small and have no effect on the bird. If for some particular reason you're in a transformer station and a high voltage line falls to the ground beside you, you have to hop away from it because the ground near the wire is no longer 'ground'. Taking a step could kill you! This is because the voltage of the ground at one of your feet could be thousands of volts different from the voltage at the ground at your other!

Also keep in mind, it's the hot is not always the source of current. In fact it's only the source half the time. The neutral will gladly source current into you if you're holding onto the hot as its sinewave goes negative. Humans are 'good enough' wires but very bad batteries.

Edit: And electric current does NOT always take the path of lowest resistance. If that was true parallel circuits would not work.