This article was posted 12/08/2008 and is most likely outdated.

Interesting Question from an Engineer
 

 

Subject - Interesting Question from an Engineer

December 8, 2008
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Interesting Question from an Engineer

Mike,

I’d like to ask your opinion on compression couplings versus set screw type. I work for an A & E firm and have been an electric power engineer for 48 years, and counting.  Our company standards call for compression couplings exclusively and have for as long as I know.

 

However, contractors who I respect for their experience and integrity (which is not all of them) state that set screw fittings are equal and in some ways better than compression.  And I think I agree, at least do not disagree, as I do not and never have regarded conduits as grounds. That being the case, I see little reason for compression couplings in most of our projects which are not in areas of high vibration, long vertical runs, long distanced between supports, conduit abuse, etc.

 

Your thoughts would be welcome.

 

Thanks, Kevin Cassidy

 

Mike Holt’s Response: Kevin, I never could figure out why compression fittings were part of specifications; to me SS fitting are equal to or better than compression fittings.
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Comments
  • I certainly have seen more conduits open at compression fittings than set screw ones. I think electricians also install set screw fittings more reliably than compression fittings. It is easier to be satisfied the raceway is fully inserted into the fitting on set screw fittings. In compression fittings the ring often interferes with an easy and reliable fit. Sure electricians should be ensuring proper insertion but removing as many possible errors in the choice of fittings can help. Yes i know more than a few sparkys that are remiss in tightening set screws too. This spec has been on the books for so long that I thought that compression fittings must have come to market at the time when EMT fittings were installed with a dimpler. Even in concrete I prefer set screw Steel fittings. As for fault return path and lower impedance? I expect the compression fittings might be better the first fault but any second faults would be about equal after all the spot welds are made.

    Mike Shea

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