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Thread: Duct bank spacing?

  1. #1
    Join Date
    Feb 2008
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    Seattle, WA
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    53

    Duct bank spacing?

    Is there a requirement for spacing runs of ductbank? Before I get the 7.5" and 30" rules I need to clarify....


    We have a ton of duct bank going in and heres an example of what we have:

    - Everything is 4" conduit.
    - We have a 2x2 conduit duct bank. Details show that it is 24 inches deep and 19 inches wide of concrete
    - It shows 2 of these 2x2 duct banks going in side by side in a trench.

    However it shows no detail as to the spacing of the groups of duct bank. Herein lies my conundrum...

    In a different detail it shows the same thing however they separate the two groups in the section call out but when they go to dimension the space between the two groups of ductbank in the detail it says "distance as required".


    My question is, "What is this required distance?" There is lighting/comm/catv/power in these various ductbanks so the only thought I had is maybe TIA/EIA standards required a separate duct bank not attached to anything else.

    Does anybody have insight in the matter?

  2. #2
    Join Date
    Jul 2004
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    Texas by the Gulf, geat crab, great shrimp
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    5,407
    Quote Originally Posted by blingbling4r View Post
    Is there a requirement for spacing runs of ductbank? Before I get the 7.5" and 30" rules I need to clarify....


    We have a ton of duct bank going in and heres an example of what we have:

    - Everything is 4" conduit.
    - We have a 2x2 conduit duct bank. Details show that it is 24 inches deep and 19 inches wide of concrete
    - It shows 2 of these 2x2 duct banks going in side by side in a trench.

    However it shows no detail as to the spacing of the groups of duct bank. Herein lies my conundrum...

    In a different detail it shows the same thing however they separate the two groups in the section call out but when they go to dimension the space between the two groups of ductbank in the detail it says "distance as required".


    My question is, "What is this required distance?" There is lighting/comm/catv/power in these various ductbanks so the only thought I had is maybe TIA/EIA standards required a separate duct bank not attached to anything else.

    Does anybody have insight in the matter?
    Somewhere deep down in my memory a 3" rule between conduits emerges, but I can't tie it to anything tangible.

    Perhaps the ready-made conduit spacers are already accomplishing this rule. Look at Carlon and perhaps they have a reasoning in their techincal section, if there is any.

    Spacing of the individual banks: no clue.

  3. #3
    Join Date
    Jan 2009
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    ORLANDO FLA
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    1,245
    Well read your specs go to conduit & raceway section in 1600 . Most jobs we do do not have Data /Com /TV / FA or any systems in the same duct bank with power you can not run these in the same trench there must be 2 foot between duct banks min.
    Also there never run in parallel ever.

    If you cross a system with a power duct bank there must be 1 foot of clear space above or below the two.

    Now this is from most of our specs so dont do this you must RFI you question for your job or read your conduit & raceway section over you will find it .

    We run lots of underground on projects this is a common issue today with fiber its kinda to me unimportant but never the less it must be done .

    conduit spacers are just what they are conduit spacers they have nothing to do with this area of space this is for magnetic induced emf on systems wiring do to power near by .
    Last edited by ohmhead; 08-25-09 at 06:02 PM.

  4. #4
    Join Date
    Feb 2008
    Location
    Seattle, WA
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    53

    Spacing...

    Well yeah I've read my Div. 26 specs now 3 times and there is nothing other then "refer to engineers details". Those sound like some pretty strict specs? Are those for utility installations? This is just upgrading the infrastructure for a marina so I would imagine it would be a little lax compared to the utility's requirements.


    Its sad but I have written 5 pages of RFI before the RFI deadline because the drawings were that bad. I'm following out a 10 conduit ductbank and in the same page it drops to only 6 without any outlet anywhere! Thats just a glimpse of what I've been dealing with.

    I've yet to hear back from the engineer as to my problem so I figured if I could get some unofficial insight from you guys on here.

  5. #5
    Join Date
    Jan 2009
    Location
    ORLANDO FLA
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    1,245
    Well most projects we do the primary power and also the 600 volts and systems total project underground so yes its a tuff spec.

    Normally on most of our work its no system in with power ever .

    There is always a clear space between the different duct banks .

    Can not tell you what to do but if you isolate these you will be fine .

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