25 ohms

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Re: 25 ohms

Pierre, Dereck Thank you both. :)

Perfect example of why the Internet forums are great, I just learned I was using the equipment wrong. :eek:

I did one test directly after the other and did not change the wiring between tests.

Guess I shoulda oter reed dem directions. :eek: :D

The job specs called for a 3 point test that was performed much later, hopefully by someone that read the directions. :p

Bob
 
Re: 25 ohms

This method sounds different than the "fall of potential" test. Also, the equipment that Bryan showed looks different as well. I know that there are many different ways to measure the grounding system resistance, and it is interesting to see how this other method is performed. :cool:
 
Re: 25 ohms

The AEMC meter shown injects a small amount of current into a circuit provided it is a loop. The loop is formed by the ground rod connected to the neutral at the customer disconnect, through the neutral conductor between the disconnect and transformer (service feeder), and the utility transformer Xo bond to the pole ground. The loop is completed via earth.

The meter comes with a calibrator. It is a loop made of a square epoxy circuit board with the center being open to form a loop. You clamp the meter around one side of the square, and it should read 25 ohms.

As I stated earlier; The down side of this meter is it reads the series impedance of the rod under test and the utility ground. For example if the utility ground were 25 and the rod were 25, the meter would read 50. So IMO it can only be used as a spot check for inspection purposes only. If a accurate reading is needed a 3-or-4 point fall-of-potential method would be required.
 
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