Deep Ground Rods

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faresos

Senior Member
Hello Every one....

Can we install a 3/4" X 10ft ground rod at 40ft deep? I read this requirement and I'm not sure if it's possible.

Also, I read in the specification if we did not get the required resistance, that we should install 30ft long ground rod, do they make ground rods that long, or you think they meant the depth?

Thanks you........
 

bphgravity

Senior Member
Location
Florida
I feel the engineer (specifier) is misguided. There would need to be an extraordinary circumstance to require a ground rod that long and/or that deep. I personally cannot think of an application that would require such a thing...

There is a grounding design that keeps popping up that is sometimes called a "triode" in the radio tower industry that is used in lieu of a counterpoise system that calls for 3 - 10ft rods coupled togther to form 30' developed feet spaced 30' apart and driven in the shape of a triangle.

I guess there a few engineers out there that really like this design and specify it frequently on projects.

I would consult with the electrical engineer and ask them just what it is they are trying to acheive???
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
It is not uncommon to have an engineer call for sectional ground rods 40 or 50' long. Often you can't drive them and you have to have a hole drilled.
While the code does not require a grounding electrode system to have a specific resistance to ground, some engineers do and sometimes when they do they will specfy a deep driven ground rod.
 

bob

Senior Member
Location
Alabama
Hello Every one....

Can we install a 3/4" X 10ft ground rod at 40ft deep? I read this requirement and I'm not sure if it's possible.

Also, I read in the specification if we did not get the required resistance, that we should install 30ft long ground rod, do they make ground rods that long, or you think they meant the depth?

Thanks you........
You can connect 10 ft rods together and arrive at a rod that is 40 ft long. You do this by driving a 10 ft rod and using a coupling you can screw the rods together. You continue to do this but you reach a point where you can no longer drive the rods any deeper. Why do you need a rod 40 ft long? Lower resistance? You can achieve the same value by driving several 10 ft rods and connecting them in parallel.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
... Why do you need a rod 40 ft long? Lower resistance? You can achieve the same value by driving several 10 ft rods and connecting them in parallel.
Maybe, maybe not. That would depend on the soil conditions where the rods are being installed.
 

iwire

Moderator
Staff member
Location
Massachusetts
I have had to install 20' rods on Cape Cod MA per the engineer this was to get the rod into the Water table as that area of the cape is nothing but pure dry sand that was covered with asphalt and buildings so it would stay dry.
 

masterinbama

Senior Member
You can get rods that will thread together or "copperweld" makes one that will friction weld itself.

If you ever have to work with liquid hydrogen, you will learn to trust your engineer.
 

brian john

Senior Member
Location
Leesburg, VA
Generally when I rad spec.s like this the engineer has no clue. NOT ALWAYS, but typically.

What is the specified resistance?

Did he request a 4 point test to assist in determining an acceptable electrode for the project or did he pull this from another spec and it seemed cool, so he ran with it.?

He is asking for a particular resistance ask him to design a system based on his dreams and wishes.

A long electrode can be beneficial in the right soil, if bedrock is at 20', maybe not.
 

bob

Senior Member
Location
Alabama
I have had to install 20' rods on Cape Cod MA per the engineer this was to get the rod into the Water table as that area of the cape is nothing but pure dry sand that was covered with asphalt and buildings so it would stay dry.

I stand corrected. There are some situations that requiire longer ground rods.
 

realolman

Senior Member
one time in georgia

one time in georgia

when I was in the service, we had to drive 40' groundrods at a few locations for the 2400/4160 distribution system.

The water table down there was probably about 2' below grade.

We threaded them together and used a jackhammer to drive them .... as far as we could. Several sections ended up laying in the swamp somewhere.
 

Jim the Tech

New member
More info

More info

Just happened on this site while browsing. I have witnessed a number of changes in practices over the years.
Motorola used to have standard called R56, It gave a good reference as to what was needed. Latest Google indicates a 2008 edition.
I have found that electric utilities have good examples of what is needed. Whether or not their practices have been followed is another matter.
The main contention I have encountered is the group making the verifying tests. The best policy is to have them make the recommendations and alternatives if you hit rocks. Then bill at an hourly rate.
 

Steviechia2

Senior Member
Location
Massachusetts
I have had to install 20' rods on Cape Cod MA per the engineer this was to get the rod into the Water table as that area of the cape is nothing but pure dry sand that was covered with asphalt and buildings so it would stay dry.

I love driving ground rods on the cape. You can use your linesman pliers to drive it! :cool:
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
I feel the engineer (specifier) is misguided. There would need to be an extraordinary circumstance to require a ground rod that long and/or that deep. I personally cannot think of an application that would require such a thing...

There is a grounding design that keeps popping up that is sometimes called a "triode" in the radio tower industry that is used in lieu of a counterpoise system that calls for 3 - 10ft rods coupled togther to form 30' developed feet spaced 30' apart and driven in the shape of a triangle.

I guess there a few engineers out there that really like this design and specify it frequently on projects.

I would consult with the electrical engineer and ask them just what it is they are trying to acheive???

A triode in lieu of a counterpoise? I am skeptical. So much so that I had to do a search and came up with this:

dereckbc
03-06-04, 06:58 PM
Counterpoise is one of those definitions that should be avoided because it has no single definition. Typically it is a radio term: "Counterpoise, a conductor or system of conductors used as a substitute for earth or ground in antenna systems".

Triode doesn't make much since either. Triode is a electron tube with a anode, cathode, and controlling grid.

"Ground Rings" and "Grids" are the simplest and most effective ground electrodes to connect lightning down conductors too.

In a high rise building, the usual method of lightning protection is just simply the structural steel framework or rebar that the building is made of. It forms a faraday cage surrounding and protecting the contents inside, and discharges lightning into the foundation much like a Ufer ground.

Are you possible referring to a "Triad" or "Tri-Pod"? That is a system of three rods layed in a triangle pattern.
 

brian john

Senior Member
Location
Leesburg, VA
There is a grounding design that keeps popping up that is sometimes called a "triode" in the radio tower industry that is used in lieu of a counterpoise system that calls for 3 - 10ft rods coupled togther to form 30' developed feet spaced 30' apart and driven in the shape of a triangle.

I guess there a few engineers out there that really like this design and specify it frequently on projects.

I would consult with the electrical engineer and ask them just what it is they are trying to acheive???

They went to the school of I heard it works, or copy and paste. I once asked if three was good wouldn't a quad be better. I was given one of those looks that ARE YOU STUPID?

In my area most ground electrode systems read very low (<5 ohms), utilizing a 3 point test (multiple test on the same electrode 3 different directions). Not sure if a triangle makes any difference. But by all means it is hardly magical.
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
They went to the school of I heard it works, or copy and paste. I once asked if three was good wouldn't a quad be better. I was given one of those looks that ARE YOU STUPID?

In my area most ground electrode systems read very low (<5 ohms), utilizing a 3 point test (multiple test on the same electrode 3 different directions). Not sure if a triangle makes any difference. But by all means it is hardly magical.

Too much school, and not enough common sense. If they can't explain it, then why do they need it?

If it's deeper than 20' why not install a ground well?

Sometimes, I believe certain people just like to waste mobey....
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
They went to the school of I heard it works, or copy and paste. I once asked if three was good wouldn't a quad be better. I was given one of those looks that ARE YOU STUPID?

In my area most ground electrode systems read very low (<5 ohms), utilizing a 3 point test (multiple test on the same electrode 3 different directions). Not sure if a triangle makes any difference. But by all means it is hardly magical.

They also know nothing about radio. If an antenna design requires a counterpoise, nothing buried in the ground will provide it. Ground radials either have to be elevated, or just below the surface. 6 inches of cover is too much.

AM towers have hundreds of radials and they are very long, all extending outward from the base of the tower. That is the counterpoise for the tower, which in AM broadcast is actually the antenna or a parasitic element.

If pounding 9 ground rods would be the same as the elaborate system still employed, why bother with thousands of feet of wire painstakingly laid out?
 

tom baker

First Chief Moderator
Staff member
Mike Holt has a video showing him driving a ground rod 50 ft deep at his home office - part of a test to measure the resistance using a fall of potential method 0r applying 120V - measuring current, to determine resistance.

There may be easier ways to achieve a low resistance, such as chemical grounds. It seems like what most engineers miss is to design the grounding system based on soil resistance first, rather than require the electrician to obtain some low resistance value by driving X number of ground rods.
 

bphgravity

Senior Member
Location
Florida
My only point is that there is no evidence that a 20-ohm grounding system is any safer than a 100-ohm or even higher system...

I would guess there are millions of structures with grounding systems well above the magical 25-ohm threshold that have never been exposed to a hazard that could have been reduced or elimnated with a lower resistance grounding system.

And at the same time, there are probably millions of Lightning Portection Systems and other grounding systems that are completely successful with relatively high grounding resistance...
 
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