This article was posted 12/08/2008 and is most likely outdated.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

  • A big point seems to have received little comment in the replies to this subject: Compression fittings are NOT automatically raintight. I believe the standard changed some ±20 years ago and only the ones listed as raintight are suitable for that use. Concrete tight is another standard; and some (mostly set-screw type) require a wrap of tape to remain concrete tight.

    If you want to exclude rain, use raintight. And arrange the conduit to drain. If you want to exclude "moisture", seal the conduit on each end and dry it with something other than 80% humidity air we have in Florida! It is VERY easy to fail getting the conduit fully seated in both sides of a short compression coupling. Different manufacturers use longer steel sleeves on SS fittings, which seem to make a stronger installation.

    As always, the pressures to work faster, use lesser trained and experienced mechanics, and "just get by" can give a bad job using any material.

    Lynn Adams

    Lynn Adams
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