The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: "Ken Taylor"
Subject: Re: Ground Resistance monitor
Date: Sat, 26 Oct 2002 13:21:05 +1300
NNTP-Posting-Host: 219-88-64-2.adsl.xtra.co.nz (220.127.116.11)
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
Hang on, if the earth is "rarely if ever" tested, how do you know that "90%
of all homes exceed the 25 ohms recommendation"??
"N. Thornton" wrote in message
> I am a distributor of Residential Meter Base Surge Arrestors. These
> ;collar; devices are installed at the main electrical
> service entrance between the electric meter and the meter can. The
> basic premise is to prevent catastrophic surges from entering the
> house by limiting the amount of voltage allowed through the device and
> shunting the excess voltage to ground. The National Electric Code
> recommends a resistance level of 25 ohms or less at the service
> entrance, however, electrical inspectors rarely if ever test a ground
> as they are only required to visually inspect it. Henceforth, we know
> from practical experience that more than 90% of all homes exceed the
> 25ohm recommendation. Simply put, surge protection devices are
> rendered ineffective if a high resistance level exists at the service
> entrance. For example, in a C-1 impulse test (6kv@3ka) a service
> arrestor that has a let through voltage of 500 volts @ 25ohms will
> allow 1000 volts through @ 100ohms. A consumer can spend hundreds of
> dollars on surge protection products that for the most part will not
> work. For some strange reason I really would like to do something to
> make this situation better. Could there be a simple way to monitor
> the ground resistance and turn off a light source, if the ground
> resistance is too high. Or maybe the LED would change color (green to
> amber) when the resistance was above a preset level. Perhaps the LED
> could turn off if the ground wire became disconnected. How would I do
> this? Let me know.
> In principle is is not hard to measure earth resistnace or impedance.
> Simplest way is to put a 2nd earth spike in and measure R between
> Another way is to run some mains current to earth and see how much the
> V live to earth changes, thus finding out how much the earth rod
> voltage rises. But that should not be done in an occupied building!
> A 3rd way would be to feed (TF isolated) high frequency to the earth
> rod. The mains supply lines will have a relatively low impedance to
> earth at rf, and you cna measure the rods earth R safely this way with
> an isolated low V supply.
> I cant help thinking there is a more elegant way, but cant think of
> Regards, NT
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup