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Author Topic: Question about tower grounding  (Read 2526 times)
K4JC
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Posts: 76




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« on: October 31, 2010, 10:34:05 AM »

I know there are a lot of differing opinions out there about grounding, so I hope I don't cause too much of a stir!  Wink

I am preparing to install a 45 foot self supporting tower about 100 feet away from the house, and 130 feet from the shack. My understanding and belief is that all your grounds - tower, shack, etc. - should be tied together with the ground where your AC power goes into the house. Now with my tower being on the opposite side of the house from the AC ground (which would end up being a distance of probably 170 feet) should I worry about tying the tower ground in with the house ground? Would it be worth it? I already plan to use 4 ground rods (20 footers if I can get them) around the tower base, plus an ufer ground, as well as redundant Polyphasers (one at the tower and one at the shack entrance) on the feedlines and rotor cable. Yes it may be overkill, but being in Florida I'd rather be safe than sorry! Any thoughts?
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NZ5E
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Posts: 75




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« Reply #1 on: November 01, 2010, 06:25:08 AM »

...should be tied together with the ground where your AC power goes into the house...

The ground rod that you designate as your "single point ground" needs to be located as close to your amateur equipment as possible, not at the AC power ground location, even though it is recommended that you connect the AC power ground to your single point ground system.  Your post seems to indicate that you have the rest of the concept correct in that you ground your tower, feedlines, lightning protection equipment, radios, etc. with one lead to your single point ground.

Your situation is different than mine with your tower being located so far from your shack.  A few years ago, I installed an extensive single point ground system for my business repeater system and recently connected that same ground system to a new tower at the same location for amateur radio use.  I have the ideal situation because my radio gear is located within about 3 feet of my single point ground rod.  Everything inside the building is tied to a copper entrance panel which has 2 six inch copper straps running straight down to the single point ground rod.

I think you would be better off with more 8 feet ground rods than a few 20 feet ground rods.  Just remember to space them twice as far apart as they are long, 16 feet separation for 8 feet ground rods.  I dug shallow trenches with a backhoe in 3 different directions from the tower base and used a large diesel powered air compressor and jack hammer to drive 31 ground rods that are tied together with copper strap.
« Last Edit: November 01, 2010, 06:44:26 AM by Terry L. Browning » Logged
K0BG
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« Reply #2 on: November 01, 2010, 06:29:50 AM »

You might want to visit http://www.w8ji.com and do a search on grounding. You might be enlightened either way!
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K4SAV
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Posts: 1850




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« Reply #3 on: November 01, 2010, 09:26:05 AM »

Now with my tower being on the opposite side of the house from the AC ground (which would end up being a distance of probably 170 feet) should I worry about tying the tower ground in with the house ground? Would it be worth it?

Only if your tower gets hit by lightning.  Since you are in central Florida, the probability of that happening is pretty high.

You need to do some research on grounding systems and how they work.  I don't think a forum post can cover all you need to know.  Once you do that you will discover there is no way to protect a system from a direct strike if there is a 170 ft wire between the ground for your entrance panel (you do have one don't you), and the AC service ground rod.  They need to be very close, maybe 6 ft apart or so.  Now you have to figure out how to make that work.

W8JI has some good information on his website, and it would be worthwhile if you studied it to see how it works, but notice that he has a building dedicated to radio and has implemented a grounding system for that building.  This is not the same as installing a radio system in an existing house which has the radio ground a long ways away from the AC power service ground rod.  He didn't give  a solution for that problem.  In fact there is no solution for that problem.

As you are reading stuff, don't get confused by the single point ground term (SPG).  Probably 95% of the ham radio info on the internet uses this term incorrectly, even when the implementation of the system they are talking about may be correct.  The NEC code requires that the grounding for all wiring entering a house be connected at a single point.  That point is the AC service ground rod.  It's where the grounds for AC power service, cable TV, telephone, waterlines, and whatever else you have, all connect together.  That is your house SPG.  You can't create another SPG for the same house and still have an SPG concept.  That means the ground rod at your entrance panel has to be connected to this SPG with a very short wire for it to be considered part of the SPG.   With a long wire connecting these, you have no SPG but have a distributed ground concept and there will be significant lightning current flowing thru your house with a distributed system.  You can visualize this better if you draw a diagram of the system of grounds, and look to see where the currents go when either the tower or AC power wiring takes a lightning hit.

Jerry, K4SAV
« Last Edit: November 01, 2010, 09:27:52 AM by Jerry Montgomery » Logged
KB9CRY
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Posts: 4283


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« Reply #4 on: November 01, 2010, 12:54:25 PM »

I know there are a lot of differing opinions out there about grounding, so I hope I don't cause too much of a stir!  Wink

I am preparing to install a 45 foot self supporting tower about 100 feet away from the house, and 130 feet from the shack. My understanding and belief is that all your grounds - tower, shack, etc. - should be tied together with the ground where your AC power goes into the house. Now with my tower being on the opposite side of the house from the AC ground (which would end up being a distance of probably 170 feet) should I worry about tying the tower ground in with the house ground? Would it be worth it? I already plan to use 4 ground rods (20 footers if I can get them) around the tower base, plus an ufer ground, as well as redundant Polyphasers (one at the tower and one at the shack entrance) on the feedlines and rotor cable. Yes it may be overkill, but being in Florida I'd rather be safe than sorry! Any thoughts?


Your tower grounding is lacking.  Polyphaser recommends at minimum 75 feet of grounding radials PER tower leg with ground rods located along each radial spaced at every 2X the rod height.   Don't really need the arrestors at the tower but grounding the coax shield to the tower is recommened.

And ditto to the SPG is located at the cable entrance to the shack and that in turn is bonded to the AC ground via an outdoor path.

Whether to bond the tower to the house system is up to you.  Two of my towers, located 60 and 120 feet away, are bonded to the house grounding but the big tower located 300 feet away is not.
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K9KJM
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Posts: 2415




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« Reply #5 on: November 02, 2010, 10:28:15 PM »

All of your ground "systems" should be bonded together.

The flat copper strap mentioned earlier IS the best material to use, Available at home supply type stores in the roofing department as Roof Flashing. Usually 6" or more wide, Can be cut in half or less with a tin snips if desired. (A 10 foot long roll X 6" wide sells for about 39 bucks- That will make 40 lineal feet of 1 1/2" wide strap when cut down)
Another good material to use is soft copper tube, Sold in 50 or so foot long rolls. 3/8" is a nice size to use for grounding. About 40 bucks for a roll in most discount type home supply stores. (With the tube, You DO need to be careful to not kink it!)

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