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## [TowerTalk] Different lightning ground question.

 To: [TowerTalk] Different lightning ground question. "Dudley Chapman" Mon, 17 Jan 2005 14:17:32 -0500
 ``` Keith's comment below reminded me of a question I had about horizontal ground rods on lightning protection systems. Current wisdom seems to suggest that if it is impossible to drive ground rods vertically, that laying them out horizontally underground is the next best thing. This sounds reasonable, but I am wondering what the difference is between a horizontal ground rod and the thick bare conductor leading up to it. Both are thick copper conductors running horizontally. Another way to ask the question is, if I substituted a 10 foot piece of #8 wire for a 10 foot horizontal ground rod, what would be the difference? If there is no difference, then just bury thick wire radials and be done with it. It would save on all the worry about joints except where the wire is bonded to whatever is being protected. I do see the difference when it comes to vertical ground rods, since it's a better way to deliver copper down into the packed earth. But that horizontal case puzzles me. Dudley - WA1X ----- Original Message ----- From: "Keith Dutson" To: Sent: Monday, January 17, 2005 9:32 AM Subject: RE: [TowerTalk] There's 'ground', and then there's 'ground' > > I read Polyphaser's technical note before installing my system. There > is a > lot of discussion about soil conductivity and how adding more rods will > improve conductivity. Do you have an idea of HOW MUCH impedance would be > reduced? > > Keith NM5G There's a heck of a lot of details that can go into this, but, it's easy to establish the BEST that you can do, in a relative sort of way. If the rods are "far" apart (basically on the order of 2 rod lengths), then they're essentially independent, so the resistance of N rods in parallel is the resistance of one rod divided by N. (assuming same soil conditions, etc.) If the rods are closer together, you get less improvement, culminating in the situation where the rods are right next to each other, when the resistance isn't much lower than a single rod. The other factor to consider is the inductance of the wire(s) going to the rod(s). 1 microhenry per meter is a nice rule of thumb number to use for an isolated conductor... it might be twice or three times that, or half or a third, but it probably won't be 10 uH/meter or 0.1 uH/meter.. You can also bury rods horizontally... To a first order, it's surface area in contact with the soil that's the important thing. _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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