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B Current carrying wire

  1. May 10, 2018 #1
    Why don't wires in any circuit touch each other and get short circuited?

    If two current carrying wires carry charges in same direction then from ampere's law,can't they touch each other due to attractive forces?
  2. jcsd
  3. May 10, 2018 #2


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    The force between two wires is actually not much for practical values of current. This is why strong electromagnets need to use many turns of wire and an Iron core. two wires in a typical circuit will not even twitch. (You can do the sums if you look up Ampere's Law - see this wiki link.)
  4. May 10, 2018 #3


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    Wires are often covered in an insulating coating/cover that prevents short circuits as well. It's extremely rare to find long strands of bare conductor except perhaps in mains power lines.
  5. May 10, 2018 #4


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    That's true in principle, but in actual practice with "normal" values of current such as on a circuit board, the forces are negligible.

    However there are exceptions and very abnormal cases.
    • Short circuits in power systems cause enormous currents.
    • Large power generators need powerful restraints to keep them from flying apart.
    • Magnets in particle accelerators experience large forces.
    • The Navy's "rail gun" would fly apart if not confined.
  6. May 11, 2018 #5


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    Many years ago I was working on a large piece of equipment that was fed with 3-phase power with a drop from the ceiling. Since this was a development project, the incoming power was just three wires hanging down without a conduit. When the many-kilowatt heater switched on those three conductors became Siamese Triplets. I'm sure any finger in the way would have been removed from the previous owners hand!
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