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Author Topic: Tower Ground/Station Ground  (Read 8692 times)
NK7Z
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« on: October 12, 2012, 06:35:16 AM »

Hello,

I will be redoing my station this winter...  One of the changes is to add a tower.  With regards to grounding, what is the best course of action?  Ground at the tower, and at the entrance point to the house, just at the house, or just at the tower.

Also, what is the best way to provide a tower ground, if that is needed?  The hole is not yet dug, so I will have an opportunity to add ground rods without having to push them in. 

I have been considering adding four 1 inch copper pipes around the tower, then back-filling the hole.  I can not penetrate the tower foundation due to permit issues.
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
WX7G
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« Reply #1 on: October 12, 2012, 07:23:55 AM »

The W8JI website has a good section on tower grounding.
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NK7Z
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« Reply #2 on: October 12, 2012, 07:53:08 AM »

The W8JI website has a good section on tower grounding.
Thank you...  That one made it to my bookmarks section!
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Dave
For reviews and setups see: http://www.nk7z.net
NK7Z
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« Reply #3 on: October 26, 2012, 11:51:06 AM »

Thanks to all for the information!  I have finally decided on the station layout, and the feed lines, and grounding...  Starting to buy stuff now...  Smiley  Thanks again all!
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Dave
For reviews and setups see: http://www.nk7z.net
WA2HKA
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« Reply #4 on: November 24, 2012, 06:20:24 PM »

Please keep us posted with pictures!   Smiley
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K7MH
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« Reply #5 on: December 16, 2012, 11:26:30 PM »

Quote
Also, what is the best way to provide a tower ground, if that is needed?  The hole is not yet dug, so I will have an opportunity to add ground rods without having to push them in. 

A ground rod pounded in the bottom of the hole for the tower and welded to the rebar (also welded together) in the tower base is what I understand to be one of the best ways to provide a good ground for lightning concerns.
Also it is important to have all grounds connected to your electrical service ground.

And yes, read the article by W8JI.
There are 3 stickies in the antenna and feedline forum on QRZ.com that are worth a read that discuss ground systems.
Also, "Lightning; Taming Thor's Thunder on a Budget" by K9KJM is a good read. You'll find it in a search.
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K8AC
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« Reply #6 on: December 17, 2012, 10:41:09 AM »

Quote
I have been considering adding four 1 inch copper pipes around the tower, then back-filling the hole.

That statement caught my eye - if the tower base is put in correctly, there shouldn't be a hole to backfill!  The concrete base should be poured against undisturbed soil - no forms except for the concrete that extends above ground level. 
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AA4PB
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« Reply #7 on: December 17, 2012, 12:29:19 PM »

K8AC is right! You don't want to be "backfilling" a tower base. I'd drive in the ground rods at least 2-3 feet away from the tower base and use heavy (#6 minimum) wire back to the tower legs. You can have the end of the rods and the wire below ground if you use Cadweld to make the below ground connections.
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W9FIB
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« Reply #8 on: December 25, 2012, 08:20:06 AM »

I could not agree with the last two posters more. A tower base can actually move in the less compacted fill as wind pushes on the tower. The less compacted fill will try to be compacted by the movement. I have seen 2 times in my life where the tower actually tipped off center several degrees. And that was in less than 18" of backfill.
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NK7Z
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« Reply #9 on: December 25, 2012, 10:20:36 PM »

Hi all,

Thanks again for the information...  I was not going to back fill the tower hole, but the holes for the ground pipes...  I have been doing lots of homework, and here is what I intend on doing, unless someone comes up with a reason to not do this...

1.  Dig large hole for tower base.
2.  Construct the rebar and place in hole...
3.  Add a ground to the rebar, run up and out of the base to teh tower legs.
4.  5 feet out from each cornner drive in a 10 foot ground rod into a trench about three inches deep.
5.  Connect with #4 to all rods, Cadweld them all...
6.  Back-fill the grounding trench, not the tower hole...  Smiley
7.  Run this ground to a dissimilar metal connector to each tower legs, one for each leg, and two on one leg.
8.  Run this ground also to an external box, with a 1/8it inch copper sheet in it.  Polyphasor stuff on the sheet, coax yhrough the polyphasors...  This is a covered, sealed cable system box used to mount cable amps in... 
9.  All cables out of the box, via water sealed PVC to an underground run of Coax, and Rotor control...  I am getting a rotor Lightening arrester for the box as well...
10. Same set up as the cables enter the house, Box, copper sheet, Polyphasors etc...

I have already re-built the station inside...  It is described on my web page under Station Information...  Basically there is now a copper bus bar running the length of the desk, with tapped screw holes for every peice of equipment that can be grounded.  This will connect to the same ground entering the hose, which is also the House electrical ground, and which will be tied to the tower ground, via the Coax Shields...  Using 4000 MAX from DX Engineering... 

Question is do I create a ground look doing it this way?  Three ground sections, tied together with largish cables...  One 100 feet from the other two, which are about 7 feet from each other, so they essentially become only one ground... 
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
AA4PB
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« Reply #10 on: December 26, 2012, 05:32:26 AM »

I would suggest that you bond the two grounding plates together with a #6 or larger cable rather than depend on the coax shields. The reason is that the coax cables are typically attached with connectors and can be removed. If you were working on it and disconnected all the coax cables then, if you had a ground leakage problem, the last one could have a voltage between the connector and ground. With a dedicated grounding conductor permanently attached you ensure that the two grounding plates are always at the same potential.

I've seen a couple of installations, amateur and commercial, where the coax connectors "sparked" when being connected because of the lack of a dedicated grounding conductor.
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NK7Z
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« Reply #11 on: December 26, 2012, 05:44:03 AM »

HI,

Is that just for a DC ground?  I would like to avoid getting 150 feet of #4 copper wire...  Smiley  Could I use something like #18?
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
AA4PB
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« Reply #12 on: December 26, 2012, 06:42:17 AM »

The NEC calls for bonding conductors to be #6 or larger. It's primarily to prevent 60Hz currents from causing a voltage difference between the two grounds. For example, say your tower ground had no currents flowing in it because there is no AC equipment out there. On the other hand, an air conditioner, water heater, or something in the house has some leakage to ground. Since your ground plate is bonded to the power circuit ground in accordance with NEC requirements, your radio ground is now at a different voltage than your tower ground. When you connect that first coax shield, you get a "spark" because it connects the grounds together. You might also get a "bite" if you get your hand across the connection. The dedicated grounding wire prevents this by making sure that there is always a low-resistance conduction path between the two physically separated grounds. The larger the conductor, the lower the resistance, and the lower the voltage difference that can exist.
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NK7Z
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« Reply #13 on: December 26, 2012, 07:17:36 AM »

Well, Well...  I was worried you might say something like that...  Thought I had all the cable in house I needed...  Now off to look for some good solid #6, in 150 foot runs...  Thanks a lot for the cross check here...  This is my first tower I have put up, and I am probably being overly cautious, but given it can either fall or electrocute me, I will error on the side of caution... Smiley  I'll have three runs of Coax to the tower, all underground...  I am actually getting excited about this...  I will finally have a support in teh center of my antenna space for some wire antennas as well!

73's,
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
K2GWK
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« Reply #14 on: January 11, 2013, 07:22:11 AM »

What I did is pound four, seven foot salted ground rods in the ground around the tower foundation. I bonded them all together to the tower at a common point using two inch braid. I ran another run of two inch braid from that point into the shack to a 6 foot piece of 3/4" wide x 1/4" thick copper buss bar that is tapped with a 10-32 thread every 1". The buss bar is mounted to that back of the station table. The ground from each piece of equipment in the shack is attached to the buss bar with a piece of 1/2" braid. It seems to work well.
« Last Edit: January 11, 2013, 07:25:48 AM by K2GWK » Logged

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