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Thread: Conduit Seperation and Support

  1. #1
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    Conduit Seperation and Support

    I am working on a desin where I will have (3) 1-1/4" conduits laying side by side clamped to unistrut. Is there a table or location where I can determine the width of the unistrut needed for these conduits? I'm assuming that I need to consider the O.D. of each conduit but I'm not sure what spacing is required between conduits for clamps and installation. Would assuming a 1/2 between the O.D. of each conduits be enough for clamps and installation of the conduits.

    Also these unistrut brackets will be installed on a channel spanning between 2 beams. How often does the NEC recommend installing these unistrut brackets to support the conduit? Is there an table in the NEC?

    What is the maximum length that a 1-1/4" conduit can span between two vertical beam supports without additional support? Is this limited to just (1) 10" section of conduit or can you have a longer piece spanning between 2 beams witout any support?

  2. #2
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    Do you have a code book?
    Have you even tried to look this up?
    The information you are looking for is clear in the appropriate section of the conduit types that you are looking.
    Tim
    Master Electrician
    New England
    Yesterday's Technology at Tomorrow's Prices

    Answers based on 2011 NEC

  3. #3
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    Quote Originally Posted by Pitt123 View Post
    Is there a table or location where I can determine the width of the unistrut needed for these conduits?
    Go here for lots of info for designing strut racks.

    http://powerstrut.com/technical.html

  4. #4
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    O.k. I found the section in NEC for RMC conduit. For 1-1/4" conduit it requires the conduit to be supported every 10 ft. So the conduit will be rising up a column and then need to be routed over to another column located 25ft away. The way I read the code is that even if I support the conduit at the top of the first conduit, I will need some sort of support at 10ft from the first column in order to support the conduit spanning the two beams? Is this correct? Does the support matter weather it is a trapeaze or if a piece of channel is routed between beams with strut welded to it to support the conduit?

    Quote Originally Posted by iwire View Post
    Go here for lots of info for designing strut racks.

    http://powerstrut.com/technical.html
    Great website Iwire. So if im looking at the tables correctly the table for pipe spacing shows the required seperation between conduits running along a wireway such as 3 conduits strapped side by side on unistrut. From the chart it says that 5.5" is required between the centerline of (2) 1-1/4" conduits ( this acounts for conduit straps, bushings, etc..) so with (3) 1-1/4" conduits I'd have a total width of about 13" including the .8" between the centerline and outside of the conduit on the outer conduits?

    Am I looking at the right table and looking at it correctly? 5.5" between conduits seems like a lot. The "Application Engineering Data - Conduit Spacing" only references 2-7/16" between 1-1/4" conduits although this table references EMT conduit. Is the difference in distance here related to the fact that this is for EMT conduit?

  5. #5
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    The required spacing between the conduits on a rack is only limited by your ability to install them. You can run them touching each other if you so choose.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  6. #6
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    We start 3' then 8', leave room for more pipe, look at the whole job start to end to drop pipes off like art work.

  7. #7
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    Quote Originally Posted by infinity View Post
    The required spacing between the conduits on a rack is only limited by your ability to install them. You can run them touching each other if you so choose.
    O.k. I need to figure out the width of the rack to show on structural drawings. If they are touching like you said I'm assuming we need to leave a little room for conduit straps and installation. Would would be typical/realistic here? Then I can just use the O.D. of the conduits and the minimum spacing to determine rack width?

    I appreciate the help I've never physically laid out a conduit rack/raceway so this is a little learning curve for me.

  8. #8
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    How about spacing the conduits 4" on center on a 16" rack? That'll leave room for allthread on the sides.

  9. #9
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    Quote Originally Posted by Pitt123 View Post
    O.k. I need to figure out the width of the rack to show on structural drawings. If they are touching like you said I'm assuming we need to leave a little room for conduit straps and installation. Would would be typical/realistic here? Then I can just use the O.D. of the conduits and the minimum spacing to determine rack width?

    I appreciate the help I've never physically laid out a conduit rack/raceway so this is a little learning curve for me.


    For strut type straps a minimum of a 1" space between the conduits will still allow the installer to put the straps on. A larger space would make the strap installation even easier.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  10. #10
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    Quote Originally Posted by infinity View Post
    For strut type straps a minimum of a 1" space between the conduits will still allow the installer to put the straps on. A larger space would make the strap installation even easier.
    Not contradicting, just adding info here...

    That 1" space assumes it is easy for the installer to expand that space to about 1-3/4". A typical 2-piece strut strap is about the same width as the strut, 1-5/8", and has to be turned sideways to insert into the strut channel before engaging. The adjacent strap already installed takes up say an 1/8"... thus 1-3/4" space just to insert one side of the strap. Irrelevant if one puts the strap in before putting the conduit into position... but that's not always feasible... and we also may want to be able to uninstall the conduit at some future date without disturbing adjacent conduits.

    Another aspect to consider is adequate space for installing condulets in the runs...
    I'll never get there. No matter where I go, I'm always here.

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