Q: If a man hangs on an un-insulated wire using both his hands what will happen and why?

Physicist: Just a quick note before answering this; hanging off of power lines holds a special place simultaneously in both in the Very Long List of Stupid Things to Do and the Somewhat Shorter List of Last Things to Ever Do.  Hanging off of power lines is a very effective way to get yourself killed a lot.

Assuming the dude in question was in contact with exactly one wire, and absolutely nothing else, and wasn’t even close to touching anything else, and that the wire didn’t snap, then he’d be fine.  Getting into that situation and back out again however involves getting electrocuted pretty good.  Turns out that the voltage in power lines is high enough that it can jump a fair distance (given the chance).

Electricity is a lot like water, with electrical current being a lot like water current, and voltage being a lot like water pressure.  It turns out that for slightly obscure reasons it’s a lot more efficient to transmit electricity using low current and high voltage.  So you can think of power lines as being like big pipes that are holding slowly moving water that’s under a lot of pressure, and that are looking for any chance to “spring a leak”.

Being in a high-pressure environment isn’t so bad, but being between high and low pressures is so bad.  For example, you can dive to 250 feet (with air tanks and whatnot), and despite being exposed to lots of pressure you don’t get pushed around or hurt.  But if you try to hold back the water in a fire hose, which operates at about the same pressure, you’ll get pushed around plenty (also, point of fact, you won’t stop the water at all).

A difference in pressure will push you around, and a difference in voltage will cause electricity to flow trough you.

A difference in water pressure will push you around and, similarly, a difference in voltage will push electricity through you.

The same sort of thing is true with voltage.  If you stand on the ground you’re at the same voltage as everything around you, and there’s no need for electricity to flow through you.  And, somewhat surprisingly, if you’re dangling from a power line you’re at the same voltage as the power line and there’s no need for electricity to flow through you.  But, if you get close to anything else, the voltage difference may be big enough for the electricity to “make a break for it” and flow through you and out onto whatever you’re near.  Same thing would happen if the wire snapped; you’d become part of the wire.

Unlike a lot of the “what if” question we get, this is one that’s been tested very, very extensively, both in terms of safety and danger.  If it were dangerous to touch a power line (while not touching anything else), then there wouldn’t be many birds left (or those that were left would wise up real fast).

The birds on these power lines are exposed to the same voltage as the wires, more than 100,000 volts, but since they’re not in contact with anything at a lower voltage (like the ground) no electricity is flowing through them.

But since contacting anything else (especially another wire) is dangerous this is a serious issue for birds big enough to bridge the gap between lines.  As a result you’ll often find weirdly shaped power poles, or very widely spaced wires in areas with large birds (large flying birds that is).

In some areas specially designed power poles

In some areas specially designed power poles are in use to keep larger birds from contacting more than one wire at a time.

The people who work with power lines take a lot of precautions.  Everything is insulated, so that they don’t ever touch the wires directly, and even if they do, they’re not touching anything else that can conduct.  By the way, and I can’t emphasize this enough, as safe and fun as hanging on power lines might seem, it’s both deadly and boring.

The fire hose picture is from here and was taken during a celebration (not a protest or anything).  The bird pictures are from here and here.

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28 Responses to Q: If a man hangs on an un-insulated wire using both his hands what will happen and why?

  1. Sean says:

    There is actually a dangerous aspect of having your body at a high potential that is never discussed. Ions from the air are accelerated towards you at 1000s of eV. Here is a fantastic paper which notes this: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-18-15534
    Indeed the authors exploit the effect to produce some very nice properties in an optical fibre.

  2. Joseph Hyde says:

    Good explanation! Just want to point out that if you went to 250 feet on air it’s quite possible that you would not come back up! That is from the aptly named ‘Nitrogen Narcosis’, which not only can induce someone to laugh for nearly no reason it can and for most people reduce your sense of ‘self preservation’ quite severely. Civilian ‘Nitrox Diving’ which only used to be available to commercial divers but is now out in the ‘civilian world’ of diving may obviate that, but ‘straight air’ won’t. I’ve not dived ‘Nitrox’ so I can’t comment on it’s usefulness for such depths but I suspect that it would be ‘pushing it’, the deeper you go with it the more Oxygen Toxicity you would be exposing yourself too the longer you were down and I suppose this goes for pretty much all levels of Nitrox diving.

    Someone that’s actually done it or looked the tables up could comment more fully on this.

  3. HV says:

    Video evindence that human can indeed contact high voltage power lines: http://www.youtube.com/watch?v=tyxJ9j77wOI

  4. William says:

    Actually as the guy says he’s wearing a faraday cage, which does indeed render you pretty much immune to electricity so long as it’s built right.

  5. Joe says:

    Openining paragraph is hilarious.

  6. Trey says:

    If you are not conducting to the ground or to anything else, there is the high possibility you will get stuck to the line because of the high amount of voltage, in which case, it would fry you from the inside out. If you get shocked by a 220 volt plug, it latches on to you, I figure it would be the same with higher voltage because you will be seizing and not able to move.

  7. Freya says:

    Does the “touching nothing else” include his clothing? Would he have to be nude to survive?

  8. The Physicist The Physicist says:

    It would make a better story, but no; you don’t have to be nude to survive. The important question is, “is there any way for the electricity to make it to ground or the other wire?”

  9. Mehrdad says:

    There is another potential danger of being charged up, then discharged when coming into contact with ground, just like static electricity. But as human body is not a huge metallic shell, I presume it takes tens of Megavolts to charge a man to a dangerous point.

  10. Fanboy says:

    If diving to 250 ft(approx 80 m) on air you will experience a pressure equal to 9 atmospheres (I.e.9 bar) that will kill you from oxygen toxicity long before you become incapable of reason through the narcotic effect of nitrogen at 9 times surface partial pressure. Nitrox, or oxygen- enriched air, will only make you die at an even shallower depth. The only safe way to dive beyond 50 m is to use mixed gas where helium is used as an inert diluting gas thus reducing the partial pressures of both oxygen and nitrogen in the breathing gas to safe levels.

  11. Bob Hildebrand says:

    It would seem to me that holding on to a 250,000 volt 60 Hz line you would look like an electrically short antenna. You would transmit 60 Hz, not efficiently, but probably leathaly. Thats why guys who work on these lines wear faraday cage suits.

  12. i wonder says:

    What would happen if someone is touching two different (hot) wires at the same time but not getting grounded? With different hands for example.

  13. The Physicist The Physicist says:

    If there’s a voltage difference between them, then current will flow from one hand to the other through the arms and body of the person involved.

  14. i wonder says:

    Ok thanks!

    I know that this may be a stupid question, and I think that you kinda answered it already but: what would happen if someone would get ac and dc voltages to his/hers body at the same time? For example touching a hot ac wire (again) and something with dc voltages (from battery or something).

    Is it possible that those different currents would interact with each other in the body even if person wouldn’t be grounded?

    And I’m sorry if this question sounds silly but that just came into my mind. And english isn’t my mother tongue so I hope you get the point. 🙂

  15. Roy says:

    Being connected to one A/C source of electrical current and one source of D/C current would be like being shot from two different guns from two different directions. They can both kill you, and they don’t in any way cancel each other out.

    Not recommended if your goal is to die of old age.

  16. Murali Krishna says:

    Have considered the electrical currents flowing in the human body due to electrostatic induction(because of high voltage AC)and electromagnetic induction (because of AC current flow)? Persons who do hotline work are protected by suits.Birds also may not be effected because of their small size. But, wouldn’t a person not wearing a protective suit be affected adversely?

  17. saqib says:

    What if a person has only one hand contact with wire and hanging in air .would current flow through him ?

  18. ritchy13 says:

    i think that you are wrong Mr the physicist!at least this is not the adequate explanation…
    the potential difference between his two hands will be wide enough to allow a considerable amount of current to flow as compared to the small distance between the legs of the bird…so this fellow will surely die! if we talk of a potential difference that is nearly the same as the amount of voltage in the wire, then we would assume that there is a leak to the ground.. this would mean simply death

  19. ritchy13 says:

    ANS to saqib: the ans is negligible… it would be the same as birds..the distance between the legs of the bird is so small that the there will be a small potential difference = small current flow. thus the man will not be shocked to death.
    on the other hand holding the wire with two hands will generate a large potential difference that will force a large current into the body of the man..

    go and see the functioning of a potentiometer..(radio volume knobs) you will understand

  20. lakshman ku.ar says:

    I have talk little much of English but your explanation is very helpful for us.

  21. prakruti says:

    i didnot got a proper answer about the hanging

  22. NXTangl says:

    @ritchy13, you are incorrect–you’d have to have your hands very, very far apart before any significant voltage drop happened. Remember, the whole point of high-voltage lines is to transfer maximum power with very little current. Since V = I * R, the voltage drop across a length of wire is equal to the current times the resistance. Copper is a pretty good conductor, and the current flowing through high-voltage power lines is very deliberately minimized in order to reduce line lossage, so a short wire like that will have a very low voltage drop–certainly not enough to induce lethal current through the much higher resistance of the human body.

  23. Narendra says:

    if the person fly and put the 33kv line at one hand with out touching ground and another line at the time he is shocked or not and one thing same like putting both hands at the time shocked or not

  24. acme fixer says:

    The explanation doesn’t consider the free space capacitance and inductance. birds have low enough FSC (free space capacitance) that they can sit on a 12 thousand volt power line with no effect, but when the voltage is ten or more times that, they seem to avoid the line. Humans (and other larger objects) have higher FSC and are affected much more as the Alternating Current charges and discharges their FSC, causing more Alternating Current to flow through their body.

    The men and helicopters that do maintenance on the 240 thousand volt AC lines are not near anything but the wire, but their FSC is enough to cause an 8 inch or 20 cm arc between the wire and the probe they use to equalize the voltage between the man / helicopter and the wire. As soon as that happens, the man can safely move from the helicopter to the wire to do the work. You can go to YouTube and search for high voltage line maintenance and see what I’ve explained.

  25. Marc Ver Pal says:

    How about when hanging on both hands while raining? Would you be elctrocuted?

  26. Doug Barr says:

    In 1964 in Littleton Colorado, a 10 year old boy jumped from a treehouse to a high voltage line and grabbed it with both hands. He got electrocuted. He didn’t die, but lost BOTH hands (due to severe burns). Direct proof that humans can get electrocuted if they touch high power lines even if they aren’t grounded (the boy was not grounded by touching ground or tree). So do not believe that you cannot get hurt even if not grounded. Linemen that touch power lines wear special conductive clothing and follow special procedures and yes, they can do it safely.

  27. Irving says:

    Consider the whole system is line to line from the generator to the load, and you accidentally touch one line and your body is grounded to earth will you be electrocuted?

  28. Durgaprasad Nayak says:

    Very helpful for me thanks all of you

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