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Author Topic: Foundation Piering and Ground System  (Read 5219 times)
KC0KEK
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« on: October 10, 2012, 09:31:20 AM »

In a few months, I'll have part of my foundation piered due to settlement, For a variety of reasons, most of the work will be done from the inside, which is a finished basement. The piering process involved cutting a hole in the slab, running a pier down to bedrock or solid soil and then filling the hole with concrete: www.foundationrepairofmissouri.com/foundation-repair/foundation-repair-products/pier-system.html.

My shack is in the area that will be piered. I'm looking for input regarding the pros and cons of using this project as an opportunity to install a ground system. Before they fill the hole closest to my operating position, I'm considering running a ground rod into the earth as deep as I can and then leaving the top six inches or so above the slab to connect the ground cable. There's a built-in cabinet in this location now, and it will go back once the work is done, so the rod end wouldn't be sticking up where it's visible or a trip hazard.

Are there any disadvantages to this plan? If not, is it okay for the ground rod to make contact with the concrete? Also, there will be at least two pier holes by my operating position, so should I consider installing a ground round in each of them?

Thanks in advance.
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WX7G
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« Reply #1 on: October 10, 2012, 10:17:11 AM »

No to the ground rod.
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KC0KEK
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« Reply #2 on: October 11, 2012, 11:43:15 AM »

No to the ground rod.

Why not?
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WX7G
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« Reply #3 on: October 11, 2012, 07:55:07 PM »

The best lightning protection routing for antenna cables is to the AC power entrance, then to the shack. The cable shields are bonded to the AC power ground. With this topology another ground is not added between the AC power ground and the shack, or after the shack. If another ground is added in this path a lightning current path is provided through the house. A ground added in the basement would provide such a path.

But if the antenna cables enter at the shack there is already a lightning current path from the antenna, to the shack, and through the house to the AC power ground. Adding a ground rod inside the basement provides a path to ground for lightning that does reduce the lightning current through the house. However, if the antenna cables enter at the shack I think it would be better to place the ground rod(s) outside the house.

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W4LWZ
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« Reply #4 on: October 12, 2012, 06:20:24 AM »

Just remember that there can be only one ground system in a building according to the national electric code.  This means that whatever ground system that you install, either under the house or outside, it must be bonded to the power company ground.  The best place to do this is where the power comes into the building from the pole.
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N4FBW
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« Reply #5 on: October 16, 2012, 08:22:19 AM »

From what I've read , running ground rods, wires, and straps through concrete is an electrical code violation. It is always a good idea to consult a copy of the National Electrical Code when working with grounds and house wiring. Each state adopts a publication year for the NEC and then that is the 'code in force' for that state. It's also a good idea to check with your county to see if they have adopted anything different. Electrical code compliance can be tricky given all the rules and regs. I suggest contacting a reputable, licensed and bonded electrician if you have any questions. It may cost a bit of money, but this can save you a lot of trouble down the road.
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K3GM
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« Reply #6 on: October 16, 2012, 09:28:57 AM »

From what I've read , running ground rods, wires, and straps through concrete is an electrical code violation......

I think a Ufer Ground>>> http://i9.photobucket.com/albums/a96/TwoSevenRight/Ufer.jpg is a prime example of what the NEC refers to as a "Concrete Encased Electrode".
« Last Edit: October 16, 2012, 09:31:57 AM by K3GM » Logged
K1CJS
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« Reply #7 on: October 17, 2012, 04:56:03 AM »


Concrete never completely 'dries out'.  It continues to cure at a slow rate over time, and water is part of that curing process.  If your installation were to sustain a direct lightning hit with the majority of the charge going through that concrete encased ground rod, the heat of the charge being conducted could well cause a sudden expansion of the concrete compounded by steam explosions along the length of the pier, effectively destroying the pier and compromising the foundation--which could have well settled to depend on that pier for its major support.  If that happens, failure of the entire structure may be the result.

Granted, that would be a worst case scenario, but it isn't about what will happen, but what could happen.
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K3GM
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« Reply #8 on: October 17, 2012, 08:01:42 AM »

A Ufer ground utilizes the built-in rebar along with the naturally conductive properties of the concrete to provide a viable ground point. Addtionally. the soil around the concrete becomes "doped", and its subsequent rise in soil pH causes the overall impedance of the soil itself to be reduced. The concrete enclosure or foundation also increases the surface area of the connection between the grounding conductor and the surrounding soil, which helps to reduce the overall impedance of the connection.

In the cases of towers installed with limited ground space, sometimes the tower base Ufer grounds present the only grounding available.  Ufer Grounds are used in building footers, concrete floors, radio and television towers, tower guy wire anchors, light poles, etc. Copper wire does not function well as a "Ufer" ground due to the pH factor of concrete. The use of the steel rebar as a "Ufer" ground works well and concrete does not chip or flake as has been found with copper. A properly designed system of concrete and rebar makes an ideal graound system.

THAT SAID.... Ufer's are typically used on external construction or in the footers and surrounding walls of a structure, as I noted above.  What you're proposing would probably yield a ground system sufficiently better than the utility service rod located near your meter.  Essentially you're exposing the interior of your dwelling to a significant surge posssibilities.  Keep the fire outside.....
« Last Edit: October 17, 2012, 08:16:38 AM by K3GM » Logged
W8JI
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« Reply #9 on: October 17, 2012, 03:20:00 PM »

The real problem is when we install a better shack ground than the power line entrance ground, the wires through the house become a fault current path. Because of this, we want the shack ground bonded to the entrance ground with many, many, times less path impedance than the path through the house wiring or plumbing to the shack ground.

Otherwise...any surge current is mainly through house wiring.

Now if I was getting a pier near the mains meter, I might augment that ground. I can't imagine making a super low impedance shack ground, though, without have an especially good bond from it to the mains ground. I don't know what good it would do.

73 Tom

 
   
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KC0KEK
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« Reply #10 on: October 17, 2012, 04:46:31 PM »

Now if I was getting a pier near the mains meter, I might augment that ground. I can't imagine making a super low impedance shack ground, though, without have an especially good bond from it to the mains ground. I don't know what good it would do.   

As it happens, there will be a pier about 6 feet from the panels and meter. That pier also is where the shack is. So augmenting literally wouldn't be a stretch. But based on the drawbacks that the other posts identify, I'm leaning toward using the existing meter ground.

Thanks, everyone.
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