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If a man holds and hangs from the power cable of trains with one hand, will he be alive or will he die if he holds and hangs from the electric wire using two hands without touching the ground ? I think in the first case he will survive as electric current does not pass through him if he holds it with one hand. But in the second case current passes through him if he holds it with two hands and he may not survive. But is the second case right ?

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    $\begingroup$ You know how birds sit on power lines all the time, with both feet, and they're just fine? It's the same thing. $\endgroup$ – zwol Apr 30 '16 at 20:51
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    $\begingroup$ He's safe until a train comes. $\endgroup$ – WGroleau Apr 30 '16 at 20:55
  • $\begingroup$ Have a look at physics.stackexchange.com/questions/249201/… $\endgroup$ – jim Apr 30 '16 at 21:10
  • $\begingroup$ Just to put numbers to this, the BART system in the San Francisco Bay Area runs at 1 kV DC, and a 5 car train draws around 2 MW when accelerating (4x 150 hp. motors per cars), which gives a draw of around 2 kA. A typical 3rd rail resistivity is around 0.01 $\Omega$/km. and with an arm span of 6' (say 2 m), this gives about 0.04 V. $\endgroup$ – copper.hat May 1 '16 at 3:50
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An easy way to determine whether there's current passing through the person or not is to look at the voltage difference between the two points that this person connects to the circuit. Because the difference in voltage is the reason of current passing through. (Same as no water pressure difference, no water flow)

When touching a wire with two hands, because the resistance of wire is close to zero, the voltage difference is also negligible. Therefore, the person is safe because there's no current passing through him.

As an extension, if the person touches two different wire with two hands at the same time instead, he will most likely get electric shock, because of the voltage difference is not zero. A grounded person touched a wire with one hand will get shocked is based on the same reason.

Hope it helps :)

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The man will NOT die in both the cases. Lets see it from the perspective of current. Imagine that you are the current travelling in the wire. You have to move from point A to point B (Let A and B be the position of contact of the man's hand with the wire) . You have 2 choices. First, you can go through the wire with low resistance to stop you. Second , you have a choice to go through the man's body which has a comparatively high resistance. So which path would you choose? Definitely the path with least resistance ,i.e., the wire. Similarly the current will do the same. Hope this answers your question.

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  • $\begingroup$ But why will he die if he touches the ground while holding the wire ? $\endgroup$ – Soubhadra Maiti Apr 30 '16 at 18:15
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    $\begingroup$ Because, his body then acts as a conductor from the wire to the earth, which are at a potential difference. A highly conducting path is formed between the wire and the earth. $\endgroup$ – vbj Apr 30 '16 at 18:17
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    $\begingroup$ @SoubhadraMaiti Yes, he will die (if he's lucky) youtube.com/watch?v=l2hPsNTFQjo (warning graphic content) $\endgroup$ – user56903 Apr 30 '16 at 18:43
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In addition to Zeeshan's answer, if you consider there is almost zero resistance between the points our hypothetical man is gripping, then there is no difference in the electrical potential between those two points. There is, therefore, no electromotive force (voltage) to drive a current through the man's body.

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