Problems understanding "electrically common" points

Discussion in 'General Electronics Chat' started by haiyyu, Mar 2, 2012.

  1. haiyyu

    Thread Starter New Member

    Mar 2, 2012
    2
    0
    Hello.

    I have been reading the E-Book for a while now.
    Currently I'm trying to understand this chapter: http://www.allaboutcircuits.com/vol_1/chpt_3/3.html

    On this page there is the following picture:
    [​IMG]
    It is said that the ground wire will make the lower part of the circuit electrically common with ground, meaning that there is no voltage drop.
    That is the part I don't understand. Why/How is it made electrically common to earth ground? As far as I understood, two points are electrically common if there is no resistance between them and thus no voltage drop. But isn't earth a bad conductor? I'm really having problems understanding that part and I would really appreciate it if someone could explain it to me.

    Thanks in advance!
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    The connection drawn from the foot of the person to the voltage sources ground being high or low resistance, e.g. a grounded metal pipe for plumbing or dry soil, doesn't make a difference.

    Replace the hand-to-ground connection with a zero Ohm resistor and the foot-to-ground connection with a high or low resistance value. There will be no voltage difference between foot and hand, therefore no current.

    If you cut the ground return wire while the person is still holding it then there will be current flow through this person and depending on the foot-to-ground resistance the person will be very unhappy.
     
    Last edited: Mar 2, 2012
  3. haiyyu

    Thread Starter New Member

    Mar 2, 2012
    2
    0
    Thanks for your reply.
    I still have some problems, though.
    What exactly do you mean by hand-to-ground and foot-to-ground connection? Which ground are they connected to?
    I'm trying to understand your example. I'd really appreciate it if you could post a simple schematic for that. Sorry if that's really simple stuff, but being a beginner it's still hard to grasp for me.
     
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