[TowerTalk] Grounding system design for new tower

[Craig Sande]

Finally, I have received my building permit for my tower and home remodel and am excavating for the tower, a 70 foot crank-up by Tashjian Towers.  The base will be located at the inside corner of a U-shaped home (visualize the lower right inside corner of the "U"), approximately 8-10 feet from adjacent walls.  The home's power panel will be located about 55 feet away (visualize the end of the upper left arm of the"U") and will utilize a new concrete garage floor with rebar as a Ufer ground.  The radio room will be located about 65 feet away from the tower (visualize the lower left outside corner of the "U").

After reading the archives and reviewing the PolyPhaser site information, I was considering the following approach to grounding my system and would appreciate any suggested modifications and good sources for material. 

The dimension of the tower base will be 4x4x8.5 feet.  I would like to extend three 52 foot radial lines away from the tower, approximately 11-12 degrees apart from one another, running away from the structure, using 1.5 inch copper strapping and an 8 foot 5/8" ground rod every 13 feet.  I'm not sure if I should take all of the radials from one leg, one from each leg, or from a strap loop interconnecting all three legs.  Also, I'm unsure how I best connect the strap to the tower and the ground rods.  I would like to use a Cadweld (or similar) connection for the ground rods because they will be covered by a new concrete patio after installation.  My tower manufacturer doesn't recommend tying into the base rebar (Ufer).  The radials may need to circumvent a large tree planter in the center of the courtyard area.  I suspect that the ground conductivity in our area isn't great, (although I have no formal measurements).

I was planning on grounding the coaxial cable ground at the top and base of the tower, although I have to figure out a good way to do this.  I would like to place a metal box at the tower base to house PolyPhaser protectors.  I wonder if that could also serve as the ground for the coax shield at the base?  Anyway, from the bottom of the box, I will have a sweep of conduit which will go underground to a hole in the homes foundation wall.  From there to the shack, the coxial cables will be on the surface of the crawl space and enter the radio room directly from the floor OR through a grounded metal plate on the wall.  I was going to use copper strapping from the tower ground to the plate and radio room equipment bus bar (copper pipe on the back side of the desk).

I also plan to run a 55 foot 1.5 inch copper strap to the home's panel ground (again a Ufer ground).  Lastly, I was going to run either #6 copper wire or again copper strapping around the house perimeter, WITHIN the crawl space, against the foundation wall, slightly buried beneath the soil if possible.  I don't think it is possible to loop a wire outside the entire house due to existing concrete pads, driveway, etc.  I hope this is ok.

Now compared to several amateur installations I have seen locally, this is overkill.  Some have advised me to put three spirals of #6 wire spanning the vertical length of hole, one for each leg, and then just pore the concrete... a Ufer type ground NOT using the rebar cage.  Some just have one to three ground rods surrounding the tower base.  Of these folks, none have had problems (so far) after many years of service.

Sorry about the long message, but I will be pouring concrete within 2-3 weeks and all of the radials will be permanently out of my reach under a new patio concrete surface!

Craig, AE7I