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Q & A: Electrical earth grounds

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Most recent answer: 03/21/2009
If a house has earth,when excess current flows,the current flows inside earth.So my question is :where inside the earth will the current flow.Does the earth bare so much of current.Doesn't the earth collapse due to this current or doesn't it face any dangerous consequences. Please answer.
- Prudhvi Raj (age 16)
Machilipatnam,Andhra Pradesh,India.
The so-called 'earth ground' is not used in practice since the resistivity of soil is so large that it becomes inefficient and impractical.  All practical electric feed lines use two wire systems.    To give you a comparison, the resistivity of copper wire is 1.7 Ω cm  whereas the resistivity of soils vary from 1,000 to tens of thousands of Ωcm depending on the amount of water, soil composition, etc.   Earth ground is used, however, in lightning rods in order to restore charge imbalance between accumulated charge in the atmosphere and the earth.  The current flow adjusts itself automatically to minimize any voltage difference.  
See for some information on soil resistivity.


(published on 03/21/2009)

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