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Ac power transmission question

  1. Nov 29, 2012 #1
    Ive never understood why outlets have 3 holes. The two at the top are the voltage in and voltage out, correct? So why is there a ground if the current already has a way to return to the voltage source through the second hole? Also, i am assuming that power lines have two cables coming from a source, one having the current flow toward the destination and one flowing in the opposite direction on the return journey? If this is correct, then why do you get shocked when you stick a paperclip into just one socket, cause the eletrons still woudnt have a path to flow through, right?
  2. jcsd
  3. Nov 29, 2012 #2
    What would happen if the hot wire got loose or worn and contacted the metal enclosure of the appliance? Touching the appliance would be the same as touching the hot wire.

    The third wire is connected to ground and the chassis of the appliance. Then if the hot wire gets loose and touches the chassis, it blows the fuse and you don't get a shock.
  4. Nov 30, 2012 #3
    Ground/earth provides a return path for the current. Either trough grounded neutral point of the transformer, grounding of your house intake cable or trough capacitances of cable or overhead power lines. (Or in the worst case scenario, trough a secondary ground fault)

    Grounding (the third wire) of appliances is mostly for safety reason, as discussed above. Ground should provide a "safe" voltage (touch potential) in case of faulty wiring. That is, no current should go trough your body, but would choose the path of least resistance trough the ground wire. Therefore good grounding structures is an important factor for electrical installations.
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