Earth Resistivity Test on concrete base

[Forum Researcher]

TL;DR Summary

I am planning to conduct an Earth Resistivity Test on my property. The issue is that my building's basement is entirely covered with concrete and pavement, and we intended to use the Fall-of-Potential test method since there are no other equipment options available for rent in my location. However, I am unable to place the probes wherever I need to take the readings.

Hi, I am planning to conduct an Earth Resistivity Test on my property. The issue is that my building's basement is entirely covered with concrete and pavement, and we intended to use the Fall-of-Potential test method since there are no other equipment options available for rent in my location. However, I am unable to place the probes wherever I need to take the readings. Therefore, I have a few questions:

• Is it possible to use the other earthing rod/pit as one of the probes?
• Does the length of the probe matter? If yes, what changes may require in calculation of resistivity?
• Is there an alternative method to perform the test without expensive equipment?
• What are the best practices for situations like these?

 

[Baluncore]

Welcome to PF.
Why do you want to measure earth resistivity?

 

[Guineafowl]

Normal method is to use two spikes and a multifunction tester:

However, if there’s concrete in the way, the best way is to measure the external loop impedance (Ze) live using the same device. That is, the loop from transformer line, through the tester, through the earth/ground path, and back to the transformer. The tester is connected between line and ONLY the earthing rod, not to the earth bar as this will introduce parallel paths via water/gas pipes etc.

I would ask, gently, that if you don’t know this, or haven’t got the test gear, should you be commissioning a supply?

 

[Forum Researcher]

Welcome to PF.
Why do you want to measure earth resistivity?

I am required to submit the earth resistivity test reports as part of the local authority's annual audit; if I don't, I will be fined.
Setting audit aside, I need to inspect the ground points in order to verify the safety of the expensive equipment as well.

 

[Guineafowl]

The L distance in the diagram above is typically 30-50m. Wouldn’t that take you outside the building to some soil where you can push in the test stakes?