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Thread: Generator and retaining walls

  1. #1
    Join Date
    Mar 2006
    Location
    Boston, MA
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    963

    Generator and retaining walls

    An architect I am working with, would like me to put a 600KW generator in an area that is pretty severely sloped. I told him it wouldn't work. So he had the civil engineer building a 7.5 foot tall retaining wall making the area flat but all my conduits will be heading in the direction of that retaining wall. So I'll have to run conduit approximately 10 feet down, make a sweep and continue on to the building being served by the generator. The whole thing is very counterintuitive to me but I guess as long as this substantial depth of conduit is for less than 25% percent of the run, it's ok.

    Still, I would be interested in your opinions and whether or not I am missing something that would trigger my shooting down the idea?

    Thanks,

    Mike
    Mike Shields, PE
    Boston, MA

  2. #2
    Join Date
    Oct 2007
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    New Jersey
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    Quote Originally Posted by mshields View Post
    An architect I am working with, would like me to put a 600KW generator in an area that is pretty severely sloped. I told him it wouldn't work. So he had the civil engineer building a 7.5 foot tall retaining wall making the area flat but all my conduits will be heading in the direction of that retaining wall. So I'll have to run conduit approximately 10 feet down, make a sweep and continue on to the building being served by the generator. The whole thing is very counterintuitive to me but I guess as long as this substantial depth of conduit is for less than 25% percent of the run, it's ok.

    Still, I would be interested in your opinions and whether or not I am missing something that would trigger my shooting down the idea?

    Thanks,

    Mike
    I'm having trouble visualizing what you have here. It sounds like the architect is having someone cut a bench into the side of a hill and you're running uphill? downhill?

  3. #3
    Join Date
    Jul 2005
    Location
    LA basin, CA
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    1,610
    I'm having visions of outdoor rated MC (Compact aluminum XHHx) or EMT strut mounted on vertical walls.
    Same way Solar array raceways feed pad-mounted inverters at base if building.
    Roger Ramjet NoFixNoPay

  4. #4
    Join Date
    Jun 2003
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    6,759
    I know there is the rule about decreasing the ampacity by 6% per foot if more than 25% of the run is deeper than standard.

    But I have a hard time believing that putting the conduit deeper makes it that much harder to get rid of heat.

  5. #5
    Join Date
    Feb 2003
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    New York, 40.7514,-73.9925
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    Quote Originally Posted by mshields View Post
    as long as this substantial depth of conduit is for less than 25% percent of the run, it's ok.
    What do you mean by that?

    I think the language in the code is 10% or 10' whichever is less.
    Ron

  6. #6
    Join Date
    Jun 2012
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    NW Ohio
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    Quote Originally Posted by steve66 View Post
    I know there is the rule about decreasing the ampacity by 6% per foot if more than 25% of the run is deeper than standard.

    But I have a hard time believing that putting the conduit deeper makes it that much harder to get rid of heat.
    Never heard that.

  7. #7
    Join Date
    Dec 2006
    Location
    Eastern Oregon
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    Most backhoes can just as easily dig 10' deep as they can 3', but now you're looking into trench boxes or sloping the ditch sides to prevent cave-ins since you're over 5'. Probably not too big of a deal if you're not going very far and someone will already be on site to cut a bench in the side of the hill.

    Just something to think about it. Other than that, I wouldn't have a problem running conduit 10' deep if we needed too.

    We had to intercept some feeder conduits 9' deep a couple years ago. No one knew they were that deep when we started digging. We kept sweeping the locator over the area as we were digging deeper just to confirm we weren't crazy and that they were actually down there!!

  8. #8
    Join Date
    Jun 2003
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    6,759
    Quote Originally Posted by mopowr steve View Post
    Never heard that.
    310.60(A)(2), but now that I look back again, that's only for conductors over 2000 volts.

    I don't see anything similar for conductors under 2000 volts, although I might have missed it.

    I have no idea why the voltage would make a difference.

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