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Friday, August 18, 2023

Question:

Hello Charlie, years ago when I was learning the trade my boss would always use the three-piece threaded coupling for joining rigid pipe together when bends wouldn't line up by just tightening it with a wrench. However, recently I ran across an electrician that said all he did was take a normal threaded coupler and then cinch it down tight after aligning the bends with a standard lock nut. Is this a common practice that meets the requirements of the NEC® for being wrench tight? Thanks in advance, Eric Bridgestone
A

Answer:

Hi Eric, great question. This comes down to the listing of the fitting(coupling). Section 300.15 requires fittings to be used only with the specific wiring methods for which they are designed and listed for use with. The installation instructions associated with a threaded rigid coupling would dictate whether the use of a locknut is allowed. Also check Section 500.8(E)(2) as rigid metal conduit installed in hazardous locations requires threaded fittings to be made up of at least 5 threads.  

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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®.

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