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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15 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.

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