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Author Topic: Oh No! Not another grounding question!!!  (Read 2163 times)
WI8P
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Posts: 260




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« on: June 10, 2013, 11:51:30 AM »

Well, yes, but only because I looked and couldn't find an answer that fits my situation.  I am putting up a tower with the required base.  The base will be about 4.5 feet in the cement.  Should I:

A) Put the ground rods in the cement (approximately 4 feet would be in the ground below the cement) and hook the straps to the tower above the cement.
B) Put the ground rods below the cement base and hook them to the tower, then pour the cement on top of everything.
C) Put the ground rods in the ground outside of the base and run longer straps on the surface of the ground.
D) Another option I haven't thought of.

I kind of like B because with the straps set in cement, I know they will never come loose, and shouldn't deteriorate from the weather.


What do you guys think?
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W9IQ
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« Reply #1 on: June 10, 2013, 02:15:20 PM »

Hi Tom,

I prefer option C. I have heard stories that putting the ground connections through the concrete have caused the concrete base to "explode" on some lightning strikes. This may be nothing more than grand rumors but considering moisture in the concrete, etc. and the fact that having the grounding outside of the concrete base creates no apparent grounding disadvantage, I personally would pick the safer route.

- Glenn DJ0IQ and W9IQ

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KB1NXE
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« Reply #2 on: June 10, 2013, 05:09:49 PM »

This is becoming my standard reply to grounding questions.  There are as many opinions out there as well, as Hams.  Grounding is something I believe you need to get knowledgeable about and make decisions that work with your location, budget and abilities.  Where do you get this knowledge?  My personal recommendation is here:  http://www.protectiongroup.com/Utility/Knowledge-Base

That's a link to the PolyPhaser site - a recognized expert and supplier of top notch protection devices.  They have a knowledge base with some of the best free training you'll ever get on grounding.  Some of it specific to Ham stations.  I ask people to read through what is there (no, you don't need to read all of it, just find what fits your situation), learn from it and apply it to your situation and budget.

FWIW, I also recommend www.georgiacopper.com for grounding strap and other stuff.  Run by a ham, the quality and price is second to none. 
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KB4QAA
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« Reply #3 on: June 10, 2013, 07:39:08 PM »

Ground rods should be outside the concrete base in undisturbed earth.  One rod for each leg.

Straps should be run across the top of the concrete base, not embedded.
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WB6DGN
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« Reply #4 on: June 10, 2013, 09:25:20 PM »

Quote
This is becoming my standard reply to grounding questions.  There are as many opinions out there as well, as Hams.  Grounding is something I believe you need to get knowledgeable about and make decisions that work with your location, budget and abilities.  Where do you get this knowledge?  My personal recommendation is here:  http://www.protectiongroup.com/Utility/Knowledge-Base

+1
He knows of which he speaks.  PolyPhaser used to publish a nice primer on the fundamentals of grounding complete with some very interesting facts about lightning however, with the site mentioned above, I doubt if the hard copy booklet is still available.  Fortunately, I've got two copies that I keep among my most useful publications.  In any case, you can't go wrong with their advice.
Tom
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K1CJS
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« Reply #5 on: June 11, 2013, 07:30:00 AM »

There is also the option of sinking the ground rods into the earth below the tower base and having them welded to the rebar cage that will support the tower base.  There IS a question in the forums pertaining to that and there were many answers to it as well.  I believe that there may be some regs that govern that, and the best thing is to check the state and local codes before making any decision. 

The national electrical code will give you the bare requirements, but state and local codes may go further, expanding on those requirements--especially on this subject.  I would recommend checking those first before checking and deciding on a method on some other website--just to find out that particular method may not be permitted where you live.
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WI8P
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Posts: 260




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« Reply #6 on: June 11, 2013, 10:24:38 AM »

This is becoming my standard reply to grounding questions.  There are as many opinions out there as well, as Hams.  Grounding is something I believe you need to get knowledgeable about and make decisions that work with your location, budget and abilities.  Where do you get this knowledge?  My personal recommendation is here:  http://www.protectiongroup.com/Utility/Knowledge-Base

That's a link to the PolyPhaser site - a recognized expert and supplier of top notch protection devices.  They have a knowledge base with some of the best free training you'll ever get on grounding.  Some of it specific to Ham stations.  I ask people to read through what is there (no, you don't need to read all of it, just find what fits your situation), learn from it and apply it to your situation and budget.

FWIW, I also recommend www.georgiacopper.com for grounding strap and other stuff.  Run by a ham, the quality and price is second to none. 


Wow - if I've read all that right, I need about 4,000 6" copper bars 30' long, all tied together with NC machined solid copper bars 4 feet thick.  I think I'll just make my tower out of copper and sink 40 feet of it into the ground!

Kidding aside, there is some great info there, but it also raises some questions that it does not answer.  For example, I didn't see any info on what gage wire to use for ground radials.  It also mentions using copper clad ground rods, but are these as good as using copper rods - or does that part matter?

One other thing they mentioned was galvanic reaction between copper grounding and steel towers causing the zinc plating to oxidize off, the steel to rust, and the tower to become unstable in as little as 20 years.  Did anyone here coat their tower base with tar or something similar to prevent this?  Would isolating the copper from the steel using stainless connectors mitigate this?
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K3GM
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« Reply #7 on: June 11, 2013, 11:25:35 AM »

When properly engineered and fabricated, concrete encased electrodes make an excellent grounds aka. Ufer grounds.  Check this example:
http://i9.photobucket.com/albums/a96/TwoSevenRight/Ufer.jpg
Concrete has a ready supply of ions and provides a better electrical ground than almost any type of soil. Over time, the soil around the concrete becomes "doped", and the rise in pH causes the overall impedance of the soil itself to be reduced. The concrete encasement also increases the surface area of the connection between the grounding conductor and the surrounding soil which helps reduce the overall impedance.  The key words here are  "properly engineered and fabricated".  This would include exothermic bonds, and a welded rebar cage (although this doesn't seem to be the case in the example picture!) Another consideration is unless your base is enormous, there is not much good in driving a number of ground rods directly under or immediately adjacent to the base as they would most likely be placed too close together and all would be subject to saturation.  Instead, think of a "field" of ground rods placed around the tower and separated the distance of their length; perhaps 3 to 4 rods per leg.  Mine are daisy chained out from each leg on the surface of the concrete.  Proper grounding is not inexpensive, and can easily approach the the budget for the stuff that's "up in the air".
« Last Edit: June 11, 2013, 12:02:16 PM by K3GM » Logged
WI8P
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Posts: 260




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« Reply #8 on: June 11, 2013, 11:37:41 AM »

When properly engineered and fabricated, concrete encased electrodes make an excellent grounds aka. Ufer grounds.  Check this example:
http://i9.photobucket.com/albums/a96/TwoSevenRight/Ufer.jpg
Concrete has ready supply of ions and provides a better electrical ground than almost any type of soil. Over time, the soil around the concrete becomes "doped", and the rise in pH causes the overall impedance of the soil itself to be reduced. The concrete encasement also increases the surface area of the connection between the grounding conductor and the surrounding soil, which helps to reduce the overall impedance.  The key words here are is "properly engineered and fabricated".  This would include exothermic bonds, and a welded rebar cage (although this doesn't seem to be the case in the example picture!) Another consideration is unless your base is enormous, there is not much good in driving a number of ground rods directly under or immediately adjacent to the base as they would most likely be place too close together and all would be subject to saturation.  Instead, think of a "field" of ground rods placed around the tower and separated the distance of their length; perhaps 3 to 4 rods per leg.  Mine are daisy chained out from each leg.  Proper grounding is not inexpensive, and can easily approach the the budget for the stuff that's "up in the air".

I am hemmed in on one side because the tower is going up next to our garage, and I only have 8 feet from the antenna to the property line on the other side.  It's a 40 foot tower, and the base will be using a Rohn 5' base section with re-rod attached in a 4' x 4' by 41/2' deep cement encasement.
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KB1NXE
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Posts: 345




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« Reply #9 on: June 11, 2013, 01:40:13 PM »

[quote author=KB1TOM link=topic=90430.msg679550#msg679550 date=1370971478
Wow - if I've read all that right, I need about 4,000 6" copper bars 30' long, all tied together with NC machined solid copper bars 4 feet thick.  I think I'll just make my tower out of copper and sink 40 feet of it into the ground!

Kidding aside, there is some great info there, but it also raises some questions that it does not answer.  For example, I didn't see any info on what gage wire to use for ground radials.  It also mentions using copper clad ground rods, but are these as good as using copper rods - or does that part matter?

One other thing they mentioned was galvanic reaction between copper grounding and steel towers causing the zinc plating to oxidize off, the steel to rust, and the tower to become unstable in as little as 20 years.  Did anyone here coat their tower base with tar or something similar to prevent this?  Would isolating the copper from the steel using stainless connectors mitigate this?
[/quote]

The acceptable minimum for ground radials is 6 gauge.  Larger, is of course better.  I was able to pick of 78 feet of 6 gauge copper on the internet for about .25 cents a foot.

The reasoning for copper clad steel ground rods is they are going to rust.  The cladding helps slow that down.  You are going to remove some of the copper while pounding the rods into the ground.  But the steel will take that pounding better than a solid copper rod or pipe!

I've heard of people using Tar to prevent Galvanic Corrosion, only to find it causes other issues (traps moisture that causes regular corrosion).  Isolation with Stainless Steel is the recommended measure to prevent it.  For instance, I put a stainless steel washer between the aluminum body of my surge suppressors and the copper bar they mount to.  My tower legs have stainless steel clamps with the copper strap sandwiched between the clamp and a stainless bar (see picture on the DX Engineering web site - it's one of their clamps).

No grounding system will be permanent.  You will need to check it at least every year (like after the snow melts) and fix/tighten/coat as needed. 
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WI8P
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Posts: 260




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« Reply #10 on: June 11, 2013, 02:04:12 PM »

Thanks KB1NXE (and others) - that helps alot, though I'm sure I'll be back with more questions!
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N6AJR
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« Reply #11 on: June 11, 2013, 02:11:21 PM »

when I did mine I just used one 8 foot rod about 3 feet to the side of my tower and a second rod a couple of feet  beyond that on the same side (it was existing) and that's what I did, so far no problems.  check the connections for corrosion now and then.
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