Electrically common between two humans

Discussion in 'General Electronics Chat' started by macro, Mar 29, 2014.

  1. macro

    Thread Starter New Member

    Mar 29, 2014
    2
    0
    Hello, I have been reading through the online allaboutcircuits book and I was just wondering about one thing in the electric safety section. The book says that two humans would be shocked if they were to both touch an ungrounded circuit. I would like to know if this is true ONLY if they touch points that are electrically uncommon or if it is true regardless of the disparity between the voltages of the points in the circuit that they come into contact with. Thanks to any reply!
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Without seeing the place you reference... (a link, page & paragraph helps!)

    For current to flow thru anything there must be a difference in voltage. That holds for wire, people, birds, everything with the sole exception of a superconductor.

    Grounding is a technique where electrical wiring is made safer if accidentally touched.

    And welcome to the forums!
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,089
    3,027
    Two humans touching is the same thing as one human, more or less, when it comes to conducting electricity.

    There was a thread here not long ago about what happens when a bird lands on a high voltage power line. The comments there might help you.

    Voltage, per se, is not an issue. All voltages are measured and expressed relative to something else, all are a ∆V. It's like the stored potential energy in a high mountain lake. Without a path to flow downhill, it doesn't matter how high it is. The energy cannot be extracted.
     
  4. macro

    Thread Starter New Member

    Mar 29, 2014
    2
    0
    Thanks for the replies guys, here is the link: http://www.allaboutcircuits.com/vol_1/chpt_3/3.html

    Near the end of the page it gives an interesting example of an ungrounded circuit, (ignore the 'accidental grounding') where if one person comes into contact with this ungrounded circuit, the person would not be shocked because he does form a path with the circuit and ground but there is no way that ground can cause the current to flow back into the circuit so he is not shocked, I believe you answered this wayneh when you said that "It's like the stored potential energy in a high mountain lake. Without a path to flow downhill, it doesn't matter how high it is. The energy cannot be extracted.".

    However, if two people touch the ungrounded circuit, again assuming there is no ground fault, they both form a path between the circuit and ground and the grounds connect to complete another path of the circuit, thereby causing both persons to be shocked by the flow of current through the grounds. What I would like to know is if the two persons are NOT shocked if they touch two points that are electrically common, where the voltage in these two points is identical. Notice in the last diagram on the page that there is a resistor between the two persons indicating a disparity in the voltages at the points they touch and this is what is vague to me. Again, thanks for any replies!
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    The image shows an ungrounded system:

    [​IMG]
    The issue here is since the system is floating (ungrounded) then ground itself is fair game as a conductor, so one person touching the system may conduct thru ground to another person touching the system.

    "Ground" is sometimes depicted as some a magical eater of electricity, but here is a case where such is not true.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,089
    3,027
    Now I finally grasp your question. The answer is that the two people, side-by-side touching the same wire, would be electrically no different than one person, and neither would be shocked.

    This is a thought experiment under "ideal" conditions. It would a dangerous experiment in real life due to non-idealities. Don't do it! ;)
     
Loading...