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From: jeffw@midas.TEK.COM (Jeff Winslow)
Newsgroups: sci.electronics,sci.physics
Subject: Re: resistance of earth ground
Message-ID: <1569@midas.TEK.COM>
Date: Mon, 29-Jun-87 18:03:36 EDT
Article-I.D.: midas.1569
Posted: Mon Jun 29 18:03:36 1987
Date-Received: Wed, 1-Jul-87 04:46:26 EDT
References: <1315@cullvax.UUCP> <327@fornax.uucp>
Reply-To: jeffw@midas.UUCP (Jeff Winslow)
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 31
Xref: mnetor sci.electronics:870 sci.physics:1793

Oh, my. Maybe I'm just dense, but...

In article <327@fornax.uucp> jl@fornax.uucp (JL) writes:

>1.) No matter HOW good the local contact, you are still limited
>    by the intervening material, which has a VERY low resistance.
                                                   ^^^
>    Even though there is a LOT of the material, the net result is 
>    a VERY VERY HIGH resistance.  We are talking >> Megaohms here! 
                 ^^^^
 
I'm confused. Are you saying it's high, or low?

>2.) If this were not true, you could well expect to electrocute 
>    a fair portion of the world any time a power-line came into 
>    good contact with the ground or water (which happens fairly 
>    often in storms that blow power lines down,...). 

Not true. All that's required to prevent electrocution is that the voltage
drop across any two points on the ground to be low enough that it doesn't
put a lethal amount of current through you if you touch them. Two of many
scenarios to satisfy this are:

1. The ground resistance is so low that most of the voltage is dropped in
the shorted line.

2. Most of the current flows below the surface (in the water table, for
instance) so that the current density at the surface, away from the point
of short, is very low.

							Jeff Winslow