National Electrical Installation Standards

Standards as High as Your Own

Thursday, January 11, 2024


Good morning, I read your forum every morning and look forward to it. We had some questions come up during a recent energy conservation meeting. We are running into a high use of spray foam insulation due to the new energy codes. Is it addressed in the NEC® as to encapsulating any wiring of any type due to the possibility of overheating. Thanks in advance, Richard P.


Hello Richard, glad to hear you are enjoying the CQD. In general, the NEC® does not prohibit the installation of NM Cable incapsulated in spray foam. There are rules pertaining to ampacity adjustment when cables are bundled in Section 310.15(C)(1). This becomes a manufacturer and product listing issue and the manufacturers of Type NM Cable do permit the cable to be encased in spray foam. This is a topic of concern that dates back to 1985, when testing was conducted by the University of Toronto on the potential overheating effects of Type NM-B Cable encased in spray foam. The findings were favorable showing maximum temperatures far below the 90º C rating of NM Cable insulation. This information can be reviewed in the NEMA Bulletin on the Thermal Effects of Residential-Installed Type NM-B Cable Encased in Spray Foam Insulation.  

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CHARLIE TROUT: 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. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

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IMPORTANT NOTICE: Unless the question requests a response based on a specific edition, all answers are based on the latest edition of NFPA 70® National Electrical Code®.

This correspondence is not a formal interpretation of the NEC® and any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, the NEC Correlating Committee any Code-making panel or other electrical technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services. 

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