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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
