National Electrical Installation Standards

Standards as High as Your Own

?
Friday, July 14, 2017

Question:

There is an argument between two engineers in the company on the use of FMC. Question arose when the contractor is trying to serve two vaccuum pumps that are more than 6 feet away. One engineer argues that NEC 348-20(A)(2) limits the use of flexible metal conduit for utilization equipment to less than 6 feet. The other engineer references paragraph 348.10 "Uses Permitted", it states that Flexible Metal Conduit, 1/2" and larger, may be installed in unlimited lengths, provided that an EGC is installed with the circuit conductors. And he also points out that the 6 ft length limitation for FMC is in reference to the U.L. rating which states that FMC in lengths over 6 ft are not approved as acceptable ground fault pathways and therefore when over 6 ft the FMC CANNOT be considered as the circuits equipment ground conductor (EGC). So, when using FMC in "unlimited lengths" as allowed by 348.10, an actual wire conductor EGC must be pulled with the circuit conductors. There have been lots of back and forth on this, and this might be a interpretation issue of the code. My question is: Who do you think is right. and what are your opinions on FMC when installed more than 6ft? Is it allowed under the condition that the engineer referenced? Sincerely, Joe

A

Answer:

Hey Joe thanks for your question. It's fun to have engineers argue but the second one is more correct. Section 348.20 applies to flexible metal conduit (FMC) that is smaller than 1/2 inch (3/8). There is no length limitation for 1/2 inch and larger sizes in 348.10.  If longer than 6 ft or the other conditions in 250.118(5) are not met then a wire type equipment grounding conductor must be installed as stated in 348.60.

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 NECA-NEIS.org for more information. NEISÔ can be purchased in three formats: as paper books, on CD, or as electronic downloads.

NECA SAFETY PRODUCTS: NECA publishes valuable electrical safety books and CDs for the industry. Visit necanet.org/store to view or purchase NECA safety products.

 CONTACT US: To submit a Code question, subscribe, or unsubscribe from this list, please e-mail: codequestion@necanet.org.