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Thread: multiple current carrying conductors in a single racway (loading the boat)

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    multiple current carrying conductors in a single racway (loading the boat)

    My question is a high level estimating question, not a granular engineering question. I understand how to calculate available fill per Ch. 9 perform adjustment factors per 310.15(B)(2)(a). When required to perform these calcs, I do so. That's not the question...

    The question is what rules can an estimator most always apply to reduce cost in regards to 'loading the boat'? I build receptacle assemblies with an average conduit length to reach a 4sq box. Then I group 3 together and sending them to the respective panel. My rule (which I'm trying to expand on) is always using 3 ckts per homerun.

    Can I apply other rules without having to perform engineering calcs? Time is short these days and I want to be as competitive as code compliantly possible.

    I made a quick sketch to show you what's in a typical assembly and the 4sq/homerun I'm wheeling off. (This sketch is drawn as if they're dedicated ckts )

    Click image for larger version. 

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    I do not do estimating, but I have a question.

    With the common disconnecting means rule (handle ties or multi pole breakers) for MWBCs how are you incorporating full boats into your estimate rules?
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Why not group 2 multi-wires together.. (2 sets of Black, Red, Blue respectively)? 9-#12s in a 3/4" pipe, then you can continue to pipe closer to their locations. I'm jumping a bit at we are considering 120/208.

    Sent from my SM-G930V using Tapatalk

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    Quote Originally Posted by jumper View Post
    I do not do estimating, but I have a question.

    With the common disconnecting means rule (handle ties or multi pole breakers) for MWBCs how are you incorporating full boats into your estimate rules?
    A 3 pole breaker costs about 3 times what 3 single poles cost. I assume that would be taken into account but it still beats the extra labor and material of non-mwbc's. I had that handle tie rule.

    I agree with knight, 9 ccc is the magic number for 14 and 12, but that is 3 full boats typically.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    I'm hesitant to answer questions on this forum in the presence of such knowledgeable members, but here goes...

    In my sketch I do share a ground but each circuit has a dedicated neutral thus not a MWBC and no need for handle ties. Typically the specs will state "no shared neutrals" which makes this crystal clear. If I wanted to really be aggressive and specs did not prohibit then I would qualify shared neutrals and wheel the homeruns as such.

    Never do I takeoff utilizing shared neutrals / MWBCs... I could ask other seasoned estimators if I should be? That would certainly save labor and materials?

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    How deep is you 4" box? A standard 1.5" deep 4" box is too small for 13-#12's.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by follybeacher View Post
    I'm hesitant to answer questions on this forum in the presence of such knowledgeable members, but here goes...

    In my sketch I do share a ground but each circuit has a dedicated neutral thus not a MWBC and no need for handle ties. Typically the specs will state "no shared neutrals" which makes this crystal clear. If I wanted to really be aggressive and specs did not prohibit then I would qualify shared neutrals and wheel the homeruns as such.

    Never do I takeoff utilizing shared neutrals / MWBCs... I could ask other seasoned estimators if I should be? That would certainly save labor and materials?
    If the specs say "no shared neutrals" then what you are doing is correct. If you want a full boat with 6 circuits with no shared neutrals, then you get into derating issues, wire size and conduit size...so yes...the cost goes up.
    However, for long home runs there is a point where it becomes a savings.

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    Quote Originally Posted by infinity View Post
    How deep is you 4" box? A standard 1.5" deep 4" box is too small for 13-#12's.
    For a homerun I would typically figure a 4x2-1/8 rather than a 4x1-1/2


    Quote Originally Posted by electrofelon View Post
    A 3 pole breaker costs about 3 times what 3 single poles cost...
    this shouldn't be forgotten. thank you


    Quote Originally Posted by cdslotz View Post
    If the specs say "no shared neutrals" then what you are doing is correct. If you want a full boat with 6 circuits with no shared neutrals, then you get into derating issues, wire size and conduit size...so yes...the cost goes up.
    However, for long home runs there is a point where it becomes a savings.
    If the specs don't prohibit this, under what circumstance would this be acceptable? Could I pack in 6 circuits into a 3/4" (6#12H, 2#12N, 1#12G, 3/4"C)? I suppose there would be de-rating, so should to simplify maybe I just use 10's? That would save an entire 3/4" raceway homerun.

    These are the tricks I'm looking to identify in this post. Something I can universally apply to some or most takeoffs.

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    Quote Originally Posted by follybeacher View Post
    For a homerun I would typically figure a 4x2-1/8 rather than a 4x1-1/2




    this shouldn't be forgotten. thank you




    If the specs don't prohibit this, under what circumstance would this be acceptable? Could I pack in 6 circuits into a 3/4" (6#12H, 2#12N, 1#12G, 3/4"C)? I suppose there would be de-rating, so should to simplify maybe I just use 10's? That would save an entire 3/4" raceway homerun.

    These are the tricks I'm looking to identify in this post. Something I can universally apply to some or most takeoffs.
    If you are sharing nuetrals then you could get nine 20A circuits in a 3/4” EMT, derate and still use #12. I usually use stranded or use 1” EMT.

    9 hots, 3 neutrals, and 1 EGC. Code wise you can use the EMT as an EGC.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jumper View Post
    If you are sharing nuetrals then you could get nine 20A circuits in a 3/4” EMT, derate and still use #12. I usually use stranded or use 1” EMT.

    9 hots, 3 neutrals, and 1 EGC. Code wise you can use the EMT as an EGC.


    I would just add that there is the "nonlinear load" thing potentially making the neuter a CCC, but everyone pretty much ignores that for branch circuits, in my experience.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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