National Electrical Installation Standards

Standards as High as Your Own

Thursday, August 31, 2023


Hello Charlie, thanks for this forum, I am always learning from your answers. (1) Can a new corner grounded delta service be installed on a building? (2) Can a corner grounded delta transformer be installed downstream from a service? (3) Can a corner grounded delta transformer be used/installed other than for a service? Thanks, John Bayduss


Hi John, thank you for the kind words regarding the CQD. Corner grounded or Grounded B phase, delta services still do exist, although availability for new service of this type of system is becoming scarce. Many utilities will support the existing services still out there, but they will not provide new service to a building. The NEC® permits these types of installation, however, there several things to consider when installing or expanding these systems. Article 200 would apply to the grounded B phase conductor of this system. Additionally, the equipment and overcurrent devices used must be rated and identified appropriately for use with a delta 3 phase system. Also see Section 240.22 for guidance on the connection of the grounded conductor to the OCPD.  

ABOUT CQD: The Code Question of the Day (CQD) is NECA and ELECTRICAL CONTRACTOR Magazine’s flagship National Electrical Code (NEC®) public forum for the industry, sponsored by EATON. The daily distribution of Q&A generates a lively dialogue and shares relative Code-based practical responses.

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CHARLIE TROUT: Charles M. Trout, better known as Charlie, was 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. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

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IMPORTANT NOTICE: Unless the question requests a response based on a specific edition, all answers are based on the latest edition of NFPA 70® National Electrical Code®.

This correspondence is not a formal interpretation of the NEC® and any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, the NEC Correlating Committee any Code-making panel or other electrical 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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