Now we'll see how to do a ground resistance measurement, using the same tester shown in the first picture in this post. For a theoretical summary just look literature for the **Wenner method** about soil resistivity, the operative scheme is shown in the following figure, where **G** is the alternate current generator, **A** the ammeter and **V** the voltmeter.

When the generator **G** leads a current in the soil, the ammeter **A** measures the current value. At the same time the voltmeter **V** measures the potential difference between electrodes number 2 and 3. Resistivity **ρ _{T}** of the soil is:

ρ_{T} = 2 π a R_{T} **(2)**

where **R _{T}** is the soil resistance shown on the

**Unilap Geo**and

**a**is the distance (in meters) between the electrodes. Using a Earth/Ground tester, different instruments like

**G**,

**A**and

**V**are replaced by just one and the soil resistance

**R**is directly shown to you.

_{T}To do an accurate measurement you should repeat it in several different places around the ground where the grounding system is located.

That's all.

Thank you!