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What is the proper way to test Ohms on a grounding electrode system using a ground rod?
What is the proper way to test Ohms on a grounding electrode system using a ground rod?
NEC sec 250.53, grounding electrodes using a ground rod requires 25 Ohms or less, and a secondary ground rod is required if the Ohms are greater than 25.
What is the correct way to test the Ohms? At the ground rod itself by using an ohmmeter with one lead on the ground rod and one lead on the bare copper connected to the main disconnect?
What if the main disconnect is located on the opposite side of the building. Would you test Ohms at the main disconnect with one lead on the bare copper going to the ground rod and one lead on the main disconnect grounding lug? Or would you still test at the ground rod location?
Thank you
1 Answer
- David BLv 47 years agoFavorite Answer
It's a little more complicated than just using an ohmmeter. The ohmmeter method won't give you a proper reading due to the low test voltage the device uses. The fall of potential method is about the best way.
The code requires 25 ohms or less. If not, all you have to do is drive a second rod to satisfy code. Due to the expense involved with the test and test equipment, it's much cheaper and easier to go ahead and drive a second rod.
Check this link out for methods that will work.
http://www.mikeholt.com/videodisplaynew.php?pageid=4134
Source(s): http://www.mikeholt.com/videodisplaynew.php?pageid=4134
