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Ground is Any Metal Surface?

  1. Apr 25, 2009 #1
    Hey, I was looking at a car and the dealer told me the battery is at the back in the trunk. When he opened the hood he showed me how I would jump it if needed or anything else. He said there is one rod (that was visible coming through a connection from the battery) for the positive and for the ground I would just connect to any metal surface on the car.

    Thinking about this can someone explain why the ground can be connected to any metal surface on the car??????

    I know the ground is just a reference point but is the ground of the battery connected to the metal surface of the car too? How does this make sense..

    Thanks!
     
  2. jcsd
  3. Apr 25, 2009 #2

    Astronuc

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    Staff: Mentor

    Ground is the reference potential with respect to the rest of the circuitry connected to it, and normally, it would refer to the potential of the earth's surface.

    On a car, the negative terminal of the battery is connected to the frame, and that is the reference potential for the electrical system in the car.
     
  4. Apr 25, 2009 #3
    so by touching the battery's positive terminal and the metal surface can and individual get electrocuted?
     
  5. Apr 25, 2009 #4

    turbo

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    Gold Member

    a potential of 12V isn't going to do much to you because your body is quite resistive. What the salesman apparently did not make clear enough is that when charging a battery or jumping a battery from another vehicle, the battery can be emitting hydrogen gas. Therefor it is safer to connect to the positive terminal first, then attach the other lead to a grounded metal part a bit distant from the battery. When the battery is charged up (or the vehicle is jump-started) the lead to ground should be removed first, and then the lead to the positive terminal. The ensures that if there is a spark upon connect/disconnect, the spark occurs some distance away from the battery.
     
  6. Apr 25, 2009 #5
    Current will flow through your body, but not enough to feel it.
     
  7. Apr 25, 2009 #6
    Okay thank you to all replies
     
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