# Unsafe ground

Discussion in 'General Electronics Chat' started by dakeeper, Jan 4, 2014.

1. ### dakeeper Thread Starter New Member

Jan 4, 2014
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Sorry for the confusing title, but I couldn't think up of a better one (and getting errors when the title is longer than 20)

I was reading http://www.allaboutcircuits.com/vol_1/chpt_3/7.html , and towards the bottom of the page it says it would be unsafe to stand on the ground with high voltage with both feet. However, from what I've been reading on the previous pages it seems to me as long as the two things you're in contact with have the same electric potential you'll be okay (i.e. bird on power line). So I was wondering, what is the reasoning for the ground to be unsafe between the downed power line and the system ground?

2. ### #12 Expert

Nov 30, 2010
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It seems pretty clear from the drawings that the earth is not at equal potentials a foot apart when a downed power line is radiating current through the dirt.

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3. ### nsaspook AAC Fanatic!

Aug 27, 2009
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I agree, the drawing is very clear.

It's the total circuit resistance and the amount of that resistance between the two feet (the bird or the person on the ground) the determines the amount of difference in electrical potential between those two feet.

The low resistance in the wire (good conductor, 10v drop) vs the 'ground' (bad conductor 2390v drop) means the potential different between points of the same distance is much greater standing on the ground than on the wire.

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4. ### dakeeper Thread Starter New Member

Jan 4, 2014
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Alright. So the voltage drop across the system ground and downed line treated as one entity is 2390 volts, but distance intervals on the ground will have their own different in voltage potentials?

EDIT: I guess I was really tired when I read through it because I missed that part entirely. Thanks guys.