Soil Resistance for Grounding Rod

[Hameedulla-Ekhlas]

Greeting to all,
Hope you all have a good time. I wanted to calculate the number of ground rod to install in grounding system for the first time. I needed the soil resistance ohm-m which is the most important parameter to determine the number of ground rod. I dont know the soil resistance and I asked Structure department about this. They had soil resistance but I am not sure, is this soil resistance that resistance which is used in ohm-m for calculating ground rod or not.

Is there any exact soil resistance for the exact type of soil. please advise me

 

[zog]

You need the actual resistance of the soil you will be installaing the rod in, given your location I would guess that it will be very high. Usually this is only done for complex ground grids, why do you need to do this?

 

[jghrist]

I dont know the soil resistance and I asked Structure department about this. They had soil resistance but I am not sure, is this soil resistance that resistance which is used in ohm-m for calculating ground rod or not.

Can you give us an example of what the Structure department gave you? They may have given you measure of soil bearing pressure capacity for foundation design. Geotechnical investigations can include electrical soil resistivity, but this would be of no concern for the Structure department. You should have resistivity values at several depths.

 

[Hameedulla-Ekhlas]

yeah, I need because the place where i am working and we are designing. We always use four rods as a square and when they test the ohm resistance it is very less.

Now I have found how to design it. Suppose, if i bury two rod parallel or three parallel or three as a triangle pr a square and its affect of configration. That is why I need the soil Resistance ohm-m to calculate the exact number of rod in a project.

Is there any predefined soil resistance for different type of soil or not please advise me.

 

[Hameedulla-Ekhlas]

its detail is not right now with me but i may give u 2moro. The hint, electrical resistivity work this is the thing i am looking for. I am searching in power system books right now to find this. If I get the predined electrical resistivity for different type soil then I will share and will discuss regarding that.

 

[Dennis Alwon]

There is no magic number for certain types of soil. I believe you will have to test the soil in the spot you want the rods. You may be able to guess and get close.

Why not use a ufer and a CEE and a ground ring and be done with it? Is this a special communications building? What is it?

 

[Hameedulla-Ekhlas]

It is a common Barrack and this Barrack contains two panels with a Sub panel.

I just want to ground these panels and sub panel. It is not a special building like hospital or communication building because such buildings need lightning protection system.

I have seen many poeple just put four rods in a three meter depth as a squar and clamps it with a insulated cable and these rods are connected with one another by a bare cable.

I want to find why we should use four rods without any calculation. I know the formula to calculate the number of rod which is needed but for this formula it is needed to have soil ohm-m resistivity.

 

[richxtlc]

You may want to try using a Wenner 4-pin tester. It uses two current probes and two voltage probes to determine the resistivity of the soil in ohms-cm. This type of instrument is used primarily for soil resistance testing, there are also some 3-pin testers that do the same and give similar results.

 

[Hameedulla-Ekhlas]

yes, sir I really respect your information. It is correct to test it by tester whether it is less than 5 ohm or more than that .


But I want its mathematically solution. I want to determine the number of rod by calculation and after that i will test it by tester whether I am right or not.

 

[Hameedulla-Ekhlas]

Thanks guys for you all information and I found what I was looking for in the below books

1- Overhead Power line ( Planning, Design Construction) by F.Kiessling.P.Nefzger
Springer.
page137 it is completely information how to find soil resistivity.

2-Power system analysis and design by B.R.Gupta

Measurement of soil resistivity and it mathematic equation and now I can find it by equation.

It has really great information about the grounding system design

 

[Hameedulla-Ekhlas]

Thanks guys for you all information and I found what I was looking for in the below books

1- Overhead Power line ( Planning, Design Construction) by F.Kiessling.P.Nefzger
Springer.
page137 it is completely information how to find soil resistivity.

2-Power system analysis and design by B.R.Gupta

Measurement of soil resistivity and its mathematic equation and now I can find it by equation.

It has really great information about the grounding system design

 

[brian john]

4-point earth resistance test as noted in a grid pattern.

http://www.aemc.com/techinfo/appnotes/Ground_Resistance_Testers/App-Ground-SoilResistivity.pdf

http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBK-GROUND-WEB.pdf