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## [TowerTalk] Polyphaser inductance calculations & grounding

 To: [TowerTalk] Polyphaser inductance calculations & grounding ad4hw@citrus.infi.net (Dan) Tue, 1 Jul 1997 21:08:39 -0400
 ```Hi OM,s While studying the Polyphaser "The Grounds for Lightning and EMP Protection" (second edition, revised 1993), I have the following observations & questions. On page 3, there is an example of a 150 foot tower that has a coax line with the shield bonded to the tower at the top and at the 15 ft point. The result is a 135 foot section of tower (36uH) in parallel with 135 feet of coax (72uH). Using the parallel inductance rule, the net inductance of this section is 24uH. The example goes on to calculate the peak voltage at the top of the tower, etc. Keep the use of the parallel inductance rule in mind as the discussion continues. On page 16, the case is made for using copper strap instead of wire for connecting ground rods because the strap has lower inductance. For example: 10 feet of #6 AWG has an inductance of 4.4uH, while 10 feet of 3 inch copper strap has an inductance of 3.0uH. Instead of using copper strap, why not use two #6 wires in parallel? (Ignore the difficulty of making connections to the wires.) I'm aware that the strap has more surface area than the wire, and that "skin effect" is a factor to be considered--but Polyphaser (if I'm reading it correctly) suggests that the primary issue here is inductance. Using the parallel inductance rule, two #6 wires in parallel would have less inductance than 6 inch wide strap! How much separation would be required between wires for the parallel inductance rule to be valid? (In the tower/coax example above, there is very little separation.) I'm not suggesting that anyone use parallel wires for grounding instead of strap. I'm asking for help in understanding this technical question and how it relates to the practical use of grounding materials. 73 & thanks! Dan Dan Long (W4TQ) 8035 Tokyo Pt. Dunnellon, FL 34433 e-mail: ad4hw@citrus.infi.net phone: 352-563-0934 -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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