National Electrical Installation Standards

Standards as High as Your Own

Wednesday, May 23, 2018


Re: CQD answer published May, May 8, 2018 - Termination Fastening

I would be far more concerned about utilizing a pressure (Bellville type) washer than I would be about the 1/2 inch vs 3/8 inch bolt. The Grade rating of the bolt/nut is also critical - Grade 5 (three lines on the head) is nearly twice that of "standard" bolts, and Grade 8 (six lines) is near three times as strong. These terminations are subject to significant thermal cycling, and the added spring force provided by the special spring washer can be critical in maintaining solid contact as the various metals expand and contract. As to the 1/2 inch vs 3/8 inch bolt question - a high quality 3/8 inch bolting is capable of providing several thousand pounds of compression force to the joint. A manufacturer might very well make the lug with a 1/2 inch hole to provide its ability to be used in various applications. Even a 1/4 inch bolt can provide large rated compression (tensile strength) : Grade 5 = 4,000 lbs, Grade 8 = 5,000.  3/8 inch Grade 5 = 9,800, Grade 8 = 12,000. I would be astounded to hear from a lug manufacturer (or U.L.) that a 3/8 inch bolting was not capable of providing adequate compression.

Thanks for the great forum of discussion. Scott Cline



Hey Scott thanks for your comments and the kind words. You are correct a key requirement is to have the appropriate amount of force that holds the connection together. A smaller bolt can do that if it has enough strength. I was hoping a pressure connector manufacturer or testing laboratory representative send in a comment specifically about the fastener size because the NEC does not have that level of detail.

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 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 to view or purchase NECA safety products.

 CONTACT US: To submit a Code question, subscribe, or unsubscribe from this list, please e-mail: