Article View: sci.electronics
Article #17697Re: resistance of earth ground
From: Jeff Winslow
Date: Mon, 29 Jun 1987 22:03
Date: Mon, 29 Jun 1987 22:03
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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
Technical Details
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Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: arc1-ca.pugleaf.net!utzoo!mnetor!seismo!rutgers!mit-eddie!uw-beaver!tektronix!teklds!midas!jeffw 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