National Electrical Installation Standards

Standards as High as Your Own

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Wednesday, May 23, 2018

Question:

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

A

Answer:

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.

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