National Electrical Installation Standards

Standards as High as Your Own

Wednesday, December 11, 2019


Re: CQD answer published Wednesday, December 4, 2019 - Service Point

I do not agree. If the transformer primary is supplied by the utility then the transformer is the service point. A grounded conductor would be required to the service disconnect.


Mike Bressler


Hey Mike thanks for your comment. It's not clear what you mean by "the transformer is the service point". The Service Point is defined in Article 100 and as explained in the Informational Note is the demarcation point, typically where ownership changes. If the customer owns the transformer then the secondary conductors are feeders and the service point is on the primary side. An illustration that is similar to what is described in the question is in the 2017 NFPA NEC Handbook as Exhibit 230.28 on page 144. You are correct that if the utility system supplying the service is grounded then a grounded conductor must be installed as stated in 250.186 but this is on the primary of the transformer. The transformer secondary needs to be installed based on the rules in 250.30 and a grounded conductor is not required but a supply side bonding jumper is.

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.

SUBMIT YOUR CODE QUESTION: Click here to submit a question to for inclusion in an upcoming edition of the Code Question of the Day, or email

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.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. NEIS can be purchased in the NECA Store in three formats: a printed or  PDF download of a standard or, as an  annual subscription service.

NECA SAFETY PRODUCTS & PUBLICATIONS: NECA produces electrical safety publications and products for the industry including jobsite safety guides, handbooks and resource kits. View a full listing of available resources and products »

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. 

UPDATE YOUR SUBSCRIPTION PREFERENCES: Subscribe or Unsubscribe from this list.