National Electrical Installation Standards

Standards as High as Your Own

Monday, January 29, 2018


Re: CQD answer published Thursday, January 4, 2018 -

I find this web site something like an opioid, I can’t stop. I understand the questioner didn’t specify a 110 volt or 220 volt feeder but I have found electricians like to serve the outbuildings 220 volt feeder using triplex, as our local utility serves our residents. The utility uses the bare messenger in the triplex as the grounded conductor and there isn’t an equipment grounding conductor. Obviously a 220 volt feeder should use quadruplex to provide for the insulated grounded conductor and the bare messenger as the equipment grounding conductor. 




Hey Dave thanks for your question, we are glad to hear that reading CQD is habit forming, in a good way. Single conductors in Table 310.104(A) are only allowed to be used as a recognized wiring method as stated in 300.3. Table 310.104 (A) includes various types of insulated conductors as that term is defined in Article 100. Triplex and quadruplex cables are covered by Article 396 as messenger supported wiring but the products typically used by electric utilities are not marked as required by 310.120.

A new definition in 396.2 for insulated conductor in the 2017 NEC indicates that "conductors encased in a polymeric material that has been evaluated for the applied nominal voltage" (triplex and quadruplex) are considered insulated if used for service conductors. They are not yet allowed for feeders and branch circuits. You are correct that an equipment grounding conductor needs to be included as stated in 250.32(B)(1).

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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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