National Electrical Installation Standards

Standards as High as Your Own

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

Do you know all the ins and outs of the Code? NECA and Electrical Contractor magazine are pleased to present their daily online feature, “Code Question of the Day.”

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    Thursday, January 19, 2017


    Can a supply duct run through a main electrical room to serve another room?

    Al Perez

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    Wednesday, January 18, 2017


    My code question for the day............

    Always been curious about & have accepted the fact that it is what it is but I've asked numerous Electrical Foreman, Project Managers & Estimators (both old & young) why is it that a two-pole single phase isn't called 2-phase as a three-pole is called 3-phase? To date, all of my answers have been ....... don't know. So I'm hoping you could answer this question for me that's been nagging at me for years.

    Thanks in advance!

    John Reynolds



    Hey John thanks for your question. The word phase is used several ways such as going through a phase during teenage years or they are out of phase (out-of-line) with something. If we use a generator as our electric supply source for example and the output is single phase then the winding or windings are "in line" or in phase. A three phase generator system has each winding 120 electrical degrees "out of phase" to the previous one. Three times 120 gives us 360 degrees in a revolution of the generator. It's not good to let something nag you for years and let us know if more explanation is necessary.

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

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.

ABOUT CHARLIE: 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. Charlie was also a member of NECA’s Academy of Electrical Contracting. Charlie’s experienced team of industry experts keep the CQD dialogue and discussions active and informative in the spirit of the man himself, as he wanted.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. Visit for more information. NEISÔ can be purchased in three formats: as paper books, on CD, or as electronic downloads.

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