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excuse me I'm newbie in electricity , can you please explain how electric will go through one cable that is connected to an earthing rod that is not connected to the circuit or the system being protected

and how the power goes in this cable will end ; will it be dissipated in earth or it will transform to another type of energy or what ?

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    \$\begingroup\$ You may need to clarify your question. For example: "electricity will go through one cable that is not connected to the same circuit from the other end". I cannot understand what this means. It would be best if you can draw a diagram. \$\endgroup\$ – Oleksandr R. Feb 23 '16 at 10:35
  • \$\begingroup\$ i modified it , is it clear now \$\endgroup\$ – Fat Mind Feb 23 '16 at 10:41
  • \$\begingroup\$ may be relevant intro question: electronics.stackexchange.com/questions/50976/… \$\endgroup\$ – MarkU Feb 23 '16 at 10:48
  • \$\begingroup\$ Also if you mean mains maybe the following: electronics.stackexchange.com/questions/211010/… \$\endgroup\$ – PeterJ Feb 23 '16 at 10:49
  • \$\begingroup\$ Huh? What? - - - \$\endgroup\$ – Olin Lathrop Feb 23 '16 at 12:45
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There is a transformer in your area which is suppling the voltage for your household. The transformer is Earthed and so when you use the earth rod there is a path between your earth and the transformer earth and the current returns to transformer and hence the circuit would be complete.

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  • \$\begingroup\$ Just to elaborate, the Earth itself is conductive. Dirt is not a very good conductor, but there is still a conductive path from the house's earth rod to the earth rod at the transformer. \$\endgroup\$ – Simon B Feb 23 '16 at 11:41
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There shouldn't be lots of electricity flowing there.

Connecting the (metal) case of a device to earth achieves two things:

  1. The case is at the same potential as anything else that is grounded, so you don't get these annoying sparks.
  2. If a cable inside the case is loose and touches the case, this connection has a lower resistance than anyone touching the case and some other ground connection.

Most of the power flowing there will be converted to heat, but since it wasn't a lot of power to begin with (except for loose cables) this effect is negligible.

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