How to do a soil/grounding system resistance measurement

In this short post we will see how to do a measurement of resistance when you have to test a grounding system and how to do a ground resistance measurement.

**Little theoretical summary**

One of the major causes of injuries and danger in the electrical systems are high failure voltages (rated value of the system plus the power surge), due to generally high failure current (look at this post) of systems. Those currents are usually drained to ground by grounding systems. It's easy to understand why you want the lowest resistance possible in the grounding system, merely:

RG = UG / IF            (1)

where RG is the grounding system resistance, IF is the failure current and UT is the voltage that a person can receive when in physical contact with the system during the failure. Obviously if you want the lowest and less dangerous UG, then you have to cut the grounding system resistance.

The resistance of the grounding system is composed by the sum of the resistance of the grounding electrode (one or more) and the whole resistance of the grounding conductor system. Therefore, we have to measure both the resistance to have the whole RG.

**End of little theoretical summary**


With the method we'll see in this post you can do a total measurement of the resistance of the grounding system in just one step, because we'll check the total resistance of the system without disconnecting the grounding electrodes. Yep!

To make those measurements you'll need a Earth / Ground Tester like the Unilap Geo / Geo X shown in the picture beside.

This tester is able to show you the value of  RG, calculating the division in (1). This tester has an integrated AC current generator, used to lead the IF current into the ground.