Current Path in Swimming Pool ?

Discussion in 'General Electronics Chat' started by morrobay, Nov 7, 2013.

  1. morrobay

    Thread Starter New Member

    Nov 7, 2013
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    A person is in a swimming pool with metal drain and ladder and the underwater
    pool lamp malfunctions with live wire in pool water contact.
    Is it correct to say they will only be shocked if they are between E source
    and drain or ladder ?
    Also what is the shape of the current path ?
     
  2. #12

    Expert

    Nov 30, 2010
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    The current path is shaped as if the water is made of trillions of 1 ohm resistors connected in a matrix. They all connect to the voltage source and the grounds, some grounds being better than others. I think people are better conductors than pool water and so, can distort the flow, in bad way. The current would tend to take a shortcut through the person that is saltier than the water, but to a limited degree. Point being, a person that is not directly in the current path can possibly distort the current path with bad results.

    Remember, it's only my opinion, and sometimes I am wrong.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    I've wondered the same thing every time I swim by one of those underwater spot lights they put in the walls of a pool.

    We had a lively discussion about this same topic - toasters in the bathtub and that sort of thing - here not long ago. There really wasn't a definitive answer except to avoid being the experimenter.
     
  4. morrobay

    Thread Starter New Member

    Nov 7, 2013
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    Thanks, is it possible to quantify a safe distance away from the current path
    between pool lamp and drain ?
    And is there a 3-D description of the shape of current path ?
     
  5. #12

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    Only if you can quantify the conductivity of the water, the conductivity of the person, the conductivity of each ground, the shape of the person, the shape of the pool, the movements of the person, etc. Now you want it in 3D? Are you going to get in the water and test the results, or maybe ask your mother-in-law to test it?

    This is getting too spooky to continue. I refuse to further describe a way to risk your life.
     
  6. morrobay

    Thread Starter New Member

    Nov 7, 2013
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  7. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Wouldn't the chlorine content of the water have some bearing on its conductivity ? and if one checked the amp-draw on the light circuit, wouldn't it be abnormal if the water were charged to ground ?

    12 is right... This is one phenom. I am certainly not going to volunteer to quantify
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Well i dont know what country your in , but the European standards are only 12Volt lights can be used in water,fed from a transformer with an RCD, so you wont get electrocuted.
     
  9. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Yeah, that makes sense... one can get quite a lot of light out of 12v nowadays... and that would hardly be fatal even if it were leaking...
     
  10. wayneh

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    It's 120V AC here in the US, as far as I can tell. See here for example, or here.
     
  11. #12

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    The link in post #6 points to a Wiki about the electric field around a multi-kilovolt substation. It points out that you can get killed by walking on seemingly dry earth if you get too close. Getting in the water with a charged electrode and some fairly good grounds is thousands of times more dangerous. Wanting a 3D map of the kill zone kind of makes my head want to explode. Much like plugging LEDs into a wall outlet, if you have to ask how, you have no business messing with it.

    I asked the moderators to lock this thread. They have not, but the good sense of the local denizens seems to be working.

    ps, Chlorine content is one of the things that increase conductivity of the water.
     
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  12. ian field

    Distinguished Member

    Oct 27, 2012
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    Your next of kin could claim a significant wedge off the pool owner if they didn't have RCD breakers on the cables to any immersed light fittings.
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    My first thought was that this will never happen because any water against the bulb will simply short across the two leads to the filament and all surge will be within the same 1 cubic inch of volume in the lamp housing. I did not consider gross mistakes by an electrician - see Hilton Hotel (Houston 2013) story attached.

    http://www.khou.com/news/local/Family-files-lawsuit-in-hotel-pool-electrocution-death-226219641.html
     
  14. #12

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    Excellent source, Gopher. Morrobay can ask the Hilton Houston Westchase, Brown Electric, and/or the Martinez family to make a 3D map of the kill zone for him.
     
  15. wayneh

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    +1 Great link.

    It certainly answers the toaster-in-the-tub question to my satisfaction. You might survive but the odds are not with you.
     
  16. GopherT

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    After thinking about it more, it is very comparable to a magnetic field. Putting a piece of iron in a magnetic field will create a preferred route for the magnetic lines of flux and induce the lines to travel into (through) the iron.

    Likewise with a more conductive object (human) in a less conductive field (pool water). Even the chlorination (calcium hypochlorite), the ionic strength of the pool water is not nearly as high as the human (0.85% sodium chloride). It is likely the electricity could be felt more and more strongly as one moves closer and closer to the direct path of the current flow. More problematic if the current can flow through the heart or brain.
     
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  17. JohnInTX

    Moderator

    Jun 26, 2012
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    My pool lights are indeed 120VAC in sealed modules. The power runs through a rubber cord that exits the light fixture through a collet-type compression fitting and runs up a pipe to above water level and on to a J-box on the wall. Perfectly safe when in good condition.

    They are connected to a dedicated GFCI-protected circuit that has caused problems over the years due to leakage in the units as well as the 'waterproof' switches that control them. Each time, I dried them out, replaced seals etc. and upgraded the GFCI. So far so good.

    It sounds like the 'electrician' either bypassed the existing GFCI to fix tripping problems or missed/ignored the fact that it was missing. Either way, I can't imagine a case where any service to an underwater, line-operated light would not include a test of the GFCI.
     
    Last edited: Nov 10, 2013
  18. #12

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    This is why we don't tell noobies how to stick an LED in a wall socket.:D
     
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  19. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    You are absolutely correct in this case! The old adage (hmmm...I guess all adages are old by definition), that electricity takes the path of least resistance is totally fallacious. It takes ALL possible paths!

    The math for volumetric conductance is extremely difficult, by the way, involving hyperbolic trigonometry in three dimensions. I've had to work out ground conductivity problems like this. Sure am glad there are simple nomographs for this. :)

    Eric
     
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  20. #12

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    Arrrgh! Where were you when we needed you?:mad:
    Just kidding. If you did do a kill zone map the moderators would have smacked your knuckles with a ruler.:D
     
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