[TowerTalk] Aluminum Hardline and Galvanized Towers

[ROBERT A. WANDERER]

     Hiya, Jay,
     
     I'm at work, so I can go a bit further with this thread.
     
     Generally, corrosion is a problem when the atomic potential 
     (nobility) exceeds +/- 0.3 Volts. The lower this value, the 
     longer corrosion takes to occur, or it can become a non-factor. 
     According to my chart (which is on page 18 of our "Grounds" 
     book), the difference between aluminum and zinc (galvanizing) is 
     (-)0.90 Volts. Personally, I don't think it's enough of a 
     difference to worry about and anything you might do may make 
     matters worse. As an example, offsetting and/or jacketing may 
     increase the likelihood of a side flash due to the potential 
     difference between the cable and the tower leg. You would 
     probably have to offset 6-9 inches to minimize the likelihood of 
     this side flash. The best thing to do is to bond the hardline to 
     the tower at the top and bottom. If the tower is greater than 
     150', bond at the 150' point and every 75-100' above that point. 
     (Well, some ham towers are >150'.) At the risk of being flamed 
     for commercializing, PolyPhaser makes appropriate products for 
     this purpose. Contact me at 800.325.7170 for more information 
     (however, give the receptionist a company name rather than just 
     saying you're an individual or a ham; without getting into the 
     subject too deeply, all hams are being summarily sent to AES.) 
     The catalog's also on-line at <www.polyphaser.com>.
     
     Hope this helps!
     
     73,
     Bob Wanderer AA0CY
     Senior Applications Engineer
     PolyPhaser Corp.

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