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From: g-rh@cca.UUCP
Newsgroups: sci.electronics,sci.physics
Subject: Re: resistance of earth ground
Message-ID: <17239@cca.CCA.COM>
Date: Mon, 29-Jun-87 01:21:58 EDT
Article-I.D.: cca.17239
Posted: Mon Jun 29 01:21:58 1987
Date-Received: Tue, 30-Jun-87 02:16:15 EDT
References: <1315@cullvax.UUCP> <327@fornax.uucp>
Reply-To: g-rh@CCA.CCA.COM.UUCP (Richard Harter)
Organization: Computer Corp. of America, Cambridge, MA
Lines: 39
Xref: utgpu sci.electronics:769 sci.physics:1711

In article <327@fornax.uucp> jl@fornax.uucp (JL) writes:
>> wolfgang@haddock.UUCP (Wolfgang Rupprecht) writes:
>> > 	What is the resistance of earth ground? Let's say we have two
>> > good connections to the earth, say two Chevettes :-), dropped into the
>> > ocean, one into the Pacific and the other Atlantic. With an ohm-meter
>> > connected between them, what kind of resistance can I expect to see?
>     ...explanation... 

>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! 

	Wrongo.  We are talking a very low resistance, namely zero.
In the old days they used a single wire for telegraph lines, relying
on the Earth to supply a return path.  Where do you think the term
ground came from, anyway.

	Although there is a lot of material, current flow through
it is in parallel (in effect.)  The surface through which the current
is spreading is a hemisphere.

	What you actually will measure is the effective electrode
impedance which is quite another matter.

>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,...). 

	Again wrong.  When a source of current in inserted into the
Earth the current density drops off as 1/R^2 (in a homogenous Earth).
When a power line comes in good contact with the Earth the current
density (and potential difference) is negligible except when you
are close to the current source.
-- 

Richard Harter, SMDS Inc. [Disclaimers not permitted by company policy.]
			  [I set company policy.]