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## Re: [TowerTalk] ground rod depth problem due to rocky soil -- solutions?

 To: towertalk@contesting.com Re: [TowerTalk] ground rod depth problem due to rocky soil -- solutions? Jim Lux Wed, 14 Nov 2012 05:00:29 -0800 mailto:towertalk@contesting.com>
 ```On 11/13/12 2:32 AM, Mike Reublin wrote: `````` On Nov 12, 2012, at 7:58 PM, Jim Lux wrote: ``````It's all about contact area... Ufer grounds work well because a 20 foot wire in a chunk of concrete has a huge contact area (a footing 20 feet long and 1x1 foot is 80 square feet, right?) `````` Wouldn't that be 20 cubic feet, or one long surface would be 20 square feet? `````` ```volume isn't the important metric.. surface area is.. a bar 20 feet long and 1x1 foot cross section is 82 square feet in cross section. ``` ```I guess, though, the top of the footing isn't usually buried, so probably 60 or so square feet.. ``` ```Concrete is almost always higher conductivity than the soil surrounding it (unless you're using some exotic low conductivity concrete) because it's hygroscopic. ``` ```So instead of a contact area between conductor (rod) and soil (probably not even a square foot), you have a fairly good contact that can't be disturbed between wire and concrete, and then a very large contact area between soil and concrete, along with the "current spreading" from the concrete, so the current density at the concrete/soil interface is low. ``` ```In fact, for RF and transients, the *capacitive* coupling from the concrete to the soil is pretty good. ``` _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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