Code Question of the Day with Charlie Trout


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The National Electrical Code is the bedrock of the electrical construction business.

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Code Question Of The Day

Friday, November 18, 2011
Question:

Subject: CQD Answer 9.30.11

Hi Charlie,

The writer says the second ground rod is to "assure" the total rod(s) resistance is less than 25 ohms. The second ground rod does not "assure" this, especially in sandy or rocky ground where you could install numerous ground rods and still not reach 25 ohms or less. The only way to "assure" the 25 ohm or less level is reached is by conducting a ground rod resistance test such as the "fall of potential method". Most electrical inspectors we encounter insist on this second ground rod thinking that it will make our installation code compliant when in fact it may not.

David A Filipiak
Sky Electric, Inc

 

Answer:

Hi David. Thanks for participating. Installing a second ground rod does make the installation Code compliant according to 250.53(A)(2) where it says a single rod shall be supplemented by an additional electrode, which can be another rod. According to the Exception to 250.53(A)(2) the additional ground rod is not required where a single rod has a resistance to earth of 25 ohms or less. However, when a second rod is installed a reading of 25 ohm is not required.

 

Section: 250.53(A)(2)
Source: Charlie Trout


ABOUT CQD: NECA’s Code Question of the Day (CQD) is Charlie Trout’s flagship National Electrical Code® forum for NECA and the industry. The CQD continues to generate a lively dialogue and relative Code-based and practical responses to an ever-increasing and interactive audience.

ABOUT CHARLIE: Charles M. Trout, better known as Charlie, is a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training.

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IMPORTANT NOTICE: All answers are based on the latest edition of the National Electrical Code®, unless the question requests a response based on a specific edition. This correspondence is not a formal interpretation of the NEC®. Any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, or any technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.

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