[Elecraft] I need some grounding-strap guidance, if'n you please

[Wes Stewart]

"One measurement is worth a thousand expert opinions"





I just used my Simpson 260 to measure from a J-bolt (that I
placed when I built half of my house) to a cold water pipe that is bonded to
both a ground rod and an AWG 4 bare copper wire buried next to the foundation
around the building periphery.
The resistance was ~10K.   So this would increase the ground strap resistance to ground by 1%, that's a few ohms in my book.
Regards,
Wes  N7WS




--- On Mon, 8/31/09, Jim Brown <jim at audiosystemsgroup.com> wrote:

From: Jim Brown <jim at audiosystemsgroup.com>
Subject: Re: [Elecraft] I need some grounding-strap guidance, if'n you please
To: "Elecraft List" <elecraft at mailman.qth.net>
Date: Monday, August 31, 2009, 11:39 PM

On Mon, 31 Aug 2009 18:34:20 -0700 (PDT), Wes Stewart wrote:

>In the overall scheme of things, a J-bolt stuck in concrete is at 
>worst a few more ohms in series with the current limiting 
resistor.

Not so. I recently poured a tower and buried three 2-inch wide 
pieces of copper in the concrete base at widely separated places 
in the base (which was roughly 30 inches square by 48 inches 
deep). The DC resistance between those straps was on the order of 
100 ohms when I measured with a Simpson 260 more than a month 
after pouring. 

I completely agree that a ground like that is plenty good enough 
to discharge a wrist strap, but it's a LOT more than "a few 
ohms."  

The purpose of the wrist strap and the anti-static mat is to pull 
you and the work to something approximating a low potential with 
respect to earth by discharging any potential that may be on you, 
the parts, or anything else. Hundreds of kOhms is probably good 
enough to do that -- our bodies are typically tens or hundreds of 
kOhms from one point to another unless we're wet, and/or grasping 
conductors quite hard, and WE are a big part of what we're trying 
to discharge! :) 

73,

Jim K9YC