Mike Dolt Enterprises
Mike Dolt Enterprises
User: klineelectric, Location: FL
Asked on: Friday, March 25, 2011 at 5:49 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:18 am EDT
Question: An inspector here is saying I have to add a ground rod to my service which is a 200 amp residential with a concrete encased electrode system (ufer ground) in a monolithic slab. I asked where in the code it says this and he says ( while arrogantly laughing at me) that if it is more than 25 ohms an additional electrode is needed. To which I said did you take an ohm reading....lol. Oh no they wont give us a ground tester, he says. Am I wrong or is the 25 ohms or less only for single rod, pipe or plate electrodes. Thats where im reading it anyway 250.56(2008 nec) or 250.53(2011nec)
You are correct. Section 250.53(A)(3) of the 2011 NEC requires an additional electrode if the resistance to ground of the grounding electrode system is greater than 25 ohms, but this requirement only applies to single rod, pipe, or plate electrodes.For concrete-encased electrode systems ( Ufer grounds), the resistance to ground is not limited to 25 ohms. Section 250.52(A)(2) of the 2011 NEC states that "made electrodes shall be permitted to be used where the soil resistivity is 100 ohm-meters or less."Therefore, you are not required to add a ground rod to your service if the resistance to ground of your concrete-encased electrode system is less than or equal to 100 ohms.The inspector is incorrect in stating that you need to add a ground rod if the resistance to ground is greater than 25 ohms. This requirement only applies to single rod, pipe, or plate electrodes.You should ask the inspector to provide you with the results of the ohm reading that he took. If he did not take an ohm reading, then he cannot require you to add a ground rod. Flag for review