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,” Sponsored by Eaton.

  • ?
    Wednesday, June 19, 2019


    Keep up the good work. I have a new project to an old plant, 1976 construction.  The power provided is 480-volt, 3 phase, open delta, B phase grounded, hopefully at the service disconnect. The NEC seems to assume that all 3 phase systems are 4 wire wye. Shouldn’t the ground be separated from the grounded phase to the transfer switch and the B phase treated as any other phase and the ground a separate wire? Should the grounded phase be connected to the line side of the motor starters and continue to the motor? Where in the code is this situation covered?

    Thanks, Have a good day!!

    Lowell I. (Laddie) Wolfe Jr.
  • ?
    Tuesday, June 18, 2019


    Re: CQD answer published Monday, June 10, 2019 -Splices in Cabinets

    Hey Charlie, Noticed that the answer to the question regarding splicing in a panelboard cabinet didn't include allowing for the conductors, splices, and taps. So, we have to include all these components when considering the permitted 75% of the space to be utilized not just the conductors. How about commenting on how one determines the space in the panelboard that is under consideration? In addition, it is common for the wiring space at the sides, top and bottom of the cabinet to differ. Thanks for considering responding to these points,

    Phil Simmons


    Hey Phil thanks for your comments. You are correct we should have provided a more complete answer. Panelboard manufacturers provide wiring space based on 408.55, including the exceptions, and meeting UL 67 the product standard for panelboards. As you mention the space at the top, sides and bottom can have different dimensions based on Table 312.6(A) and 312.6(B). Conductors are not allowed to fill the cross sectional area of the wiring space in a cabinet to more than 40% as stated in 312.8(A)(1). And the total area of conductors, splices and taps cannot exceed 75% of that cross sectional area. The NEC does not have specific details for determining the space of splicing devices so if the manufacturer does not provide dimensions making a measurement in the field can be 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.

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