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Electrical grounding and alternating current

  1. Apr 22, 2014 #1
    When households are said to be grounded using an earth wire, electrons are supposed to flow to the ground because the ground is at zero volts. For example, if your the live wire touches the metal casing of your toaster then the earth wire takes the current to ground. But isn't a lot of household current alternating? Therefore, how would current flow to ground because with alternating current there is no net movement of charge?

    With another example, what would specifically kill you if your feet were on the ground but your hands were touching an overhead cable (you would need to be tall I know). Again, no charge would flow through you specifically as it would be alternating. Would it be the ions in your body which kill you as they would be shaking back and forth due to the alternating voltage?

    Also, why is the ground considered to be a source or sink for electrons - wouldn't the ground have to be a conductor to have free electrons?

    Thank you for any help!
     
  2. jcsd
  3. Apr 22, 2014 #2

    AlephZero

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    I'm not sure why you think that is true, but suppose child is playing on a swing, and you step in front of the swing so it hits you. Would you argue that you won't get hurt by the impact, because there is no net movement of the swing, it only alternates between one direction and the other?
     
  4. Apr 22, 2014 #3

    UltrafastPED

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    An excellent discussion of AC wiring practices, and the function of each wire - the focus is on safety:
    http://amasci.com/amateur/whygnd.html

    Ask if you have further questions after studying this.
     
  5. Apr 22, 2014 #4
    Thanks for the replies. From books I have read they say that there is no net movement of electrons in a wire carrying alternating current, therefore how can an earth wire carry current away from a faulty appliance in the house?
     
  6. Apr 22, 2014 #5

    AlephZero

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    OK, maybe the use of language isn't very precise and that is confusing you. Half the time, the earth wire is carrying current away from the faulty appliance. The other half of the time, it is carrying current back to the appliance.

    Actually, even the idea of "carrying current" is misleading, because individual electrons in the wire only move back and forth by a few millimeters at most. Nothing physically moves from the appliance all the way to the ground and back again, 50 or 60 times a second. When the appliance is working normally, nothing moves all the way from the power station to your house either.
     
  7. Apr 22, 2014 #6
     
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