Grounding grid resistance measurements in concrete

[lume7006]

Hello,

I would like to receive some feedback from your experiences to perform grounding grid measurements in a existing one and you need to determine the value of the resistance, there is a layer of concrete.
How do you determine the resistance value?

I mean, do you "make some holes" to bury the electrodes?
Is this the only method to obtain correct values?

Any suggestions will be welcome.

 

[Elmir]

Measurements can be made with a layer of concrete on the surface. Concrete is a porous material, thus with the aid of water the resistivity will not be high.

Use a wire mesh to make contact with the ground when conducting measurements. Pack some moist dirt over the wire mesh, this will ensure good contact with the surface beneath to conduct measurements.

The idea is to have good contact with the earth for any type of tests regardless of surface. With higher resistivity materials you will require better equipment with higher output voltage to drive current.

Determine the resistance value by inspection of a fall of potential plot.

 

[lume7006]

Hello,

Is there any other method to determine ground resistance?

Because, according to ths standards the only "recognize" method is the "62%" but, we arenot certain if there are some alternatives to simplified this.

I thank you in advance

 

[Elmir]

The 62% method is only applicable for sites that have homogenous soil structure. 99% of sites do not have homogenous soil structure, thus the requirement to plot measurements and by inspection of the graph determine ground impedance of the ground grid under test.

I recommend hiring a qualified testing agency to perform the testing. There are many pittfalls that can be encountered.