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I am designing a ground ring for an industrial facility. We typically require the ground ring to be 5’ from the building, but I can not find anything in the NEC for a building distance requirement. Do you know if there is such a requirement and if so, how far?

Hi Sherry,

Thank you for your question regarding ground rings and required distances, it is our pleasure to help.

You are correct that the 2011 National Electrical Code (NEC) does not have a required distance that a ground ring must be placed from a building.  Currently, ground rings are only required to be in direct contact with the earth for at least 20 feet and be at least 2 AWG bare copper or larger (NEC Article 250.52(A)(4)), and must be buried at least 30 inches below grade (NEC Article 250.53(F)). 

Now, there are other standards that do have requirements for distance in regards to the installation of ground rings.  In particular, Motorola’s R56 Standard Chapter 4 Part 4.4.1.6 lists the following rules, in summary:

  • Ground rings shall be installed in direct contact with the earth at a depth of 30 inches below grade, or below the frost line, whichever is deeper (ANSI T1.334-2002, section 5.3.1 and NFPA 70-2005, Article 250.53).
  • Building ground rings shall be installed at least 3 feet from the building foundation and should be installed beyond the drip line of the roof (MIL-HDBK-419A and MIL-STD-188-124B).
  • Tower ground rings shall be installed at least 2 feet from the tower foundation (ANSI T1.334-2002, section 5.3.1).

In some cases, ground rings are installed for human safety reasons, specifically to reduce Step & Touch Voltage hazards.  When this is the case, it is often advantages to install the ground ring one (1) meter (3 ft.) from the building.  One meter is considered to be the reaching distance of a person, and helps to balance the voltage differential between the hands and the feet.  It should be noted that the Substation Safety Standard IEEE Std 80 recommends in 9.4(c) a depth of 12 to 18 inches.  Shallower  depths are important when trying to reduce Touch Voltage levels, whereas deeper depths tend to help reduce Step Voltages.

Also, 10-ft long ground rods should be placed at 20-ft intervals along the ground ring (MIL-HDBK-419A).  8-ft ground rods can be used, but are discouraged in ANSI T1.334-2002, for good reason; they have half the sphere-of-influence of a 10-ft ground rod.  Please see the following link for more information:  https://www.esgroundingsolutions.com/about-electrical-grounding/grounding-electrode-sphere-of-influence.php

We hope this information is useful to you.  Should you have any further questions, please do not hesitate to call us at 310-318-7151, someone will be glad to speak with you free of charge.

Best regards,

The Engineering Team at E&S Grounding Solutions

 

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