National Electrical Installation Standards

Standards as High as Your Own

Wednesday, April 10, 2019


Re: CQD answer published Wednesday, March 27, 2019 -Large equipment

1) Charlie, Thanks for all work that you put into CQD, I look forward to it every day! My understanding is that busway is a wiring method and that 110.26(C)(3) is intended to apply to the equipment that houses switches or breakers.  110.26(C)(3) states “equipment rated 800 A or more that contains overcurrent devices, switching devices, or control devices…”  The 1200 Amp busway itself does not include the overcurrent device, the 400 Amp bus-plug is the equipment containing the OCPD. For an 800 Amp bus-plug I would agree with the response given, but for a 400 Amp plug in unit the answer provided is not the typical understanding I’ve had about how to apply the rule in 110.26(C)(3).  I wonder if the answer would have been the same if we had a 1000A riser with cable and conduit to a tap box that is close coupled to a 200A safety switch? Thanks again. Rod West

2) Charlie, You great service to those of us who merely think we know the Code! If I may be so bold as to ask you to consider another interpretation to 110.26 (C) in reference to the 1200A bus and the 400A bus plug in the question. NEC 110.26 (C) (2) Large Equipment rated 1200A and more and over 6-feet wide that contains overcurrent devices, switching devices, etc.  This requires one door at each end of the working space unless there is an unobstructed egress or there is extra working space.  Highlighting added for emphasis. NEC 110.26 (C) (3) Personnel doors for areas with equipment rated 800A or more that contains overcurrent devices, switching devices, or control devices.  This requires personnel doors within 25-feet of the equipment to open in direction of travel and have listed panic hardware. Highlighting added for emphasis. The two sections I am referencing here hinge on the definition of “contains”. The bus in the question is an enclosure that contains only bus bars rated 1200A.  The bus plug in the question is an enclosure that attaches to the outside of the bus and contains bus, switching components, and overcurrent devices rated 400A. As I understand bus ducts, they do not contain the items that are indicated in 110.26 (C) (2) or (3).  The bus plug is rated 400A and is below 800A that would require personnel doors to meet the requirements of 110.26 (C) (3). Please consider my interpretations of the question for Tuesday, March 26. Thank you, Rodney Welch


Hey Rod and Rodney thanks for your comments and kind words - we are all constantly learning. As both of you mention, the 1200 ampere busway in the original question does not contain overcurrent devices or switching devices, the circuit breaker or fusible switch (bus plug) rated at 400 amperes does. You both have great points, because the equipment containing the overcurrent protective device (bus plug) is less than 800 amperes, the rule literally does not apply to it. Seems interesting that if this was a panelboard rated 800 amperes or more, with lower rated circuit breakers or fusible switches, the rule would apply to the panelboard, even though the cabinet the panelboard was in doesn't actually have an ampere rating.

This might be a good opportunity for a Public Input to the 2023 NEC for both 110.26(C)(2) and 110.26(C)(3) to see what Code Making Panel 1 thinks. Until then check with the AHJ for their interpretation prior to making the installation to make sure they agree.

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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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