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Thread: Sharing emergency generator and tap rule

  1. #1
    Join Date
    Jun 2007
    Posts
    723

    Sharing emergency generator and tap rule

    The hospital and nearby clinic share same emergency generator.
    The inspector came out and want hospital and clinic must have
    their own ATS. Generator's 600A main breaker, 600A feeder, hospital's ATS-E2
    and downstream panels (cyan color) have been installed.

    The clinic and its panel (yellow color) will be installed. Does anyone see
    any code violation with this tap installation to new ATS-E1? ATS-E2 does
    not have a protection downstream of 600A CB.

    The total emergency load is less than 150kVA. Thanks!

    See attached picture.
    Thank you.


    SKE.pdfClick image for larger version. 

Name:	diagram.JPG 
Views:	32 
Size:	93.5 KB 
ID:	20510

  2. #2
    Join Date
    Oct 2012
    Location
    new york
    Posts
    25
    What version of the code are you following? The clinic ATS appears to be an Article 700 load. It looks like the hospital has a combination of load types on a single ATS which isn't code compliant but assuming it's okay since it's existing. If you consider the hospital ATS also a 700 load, I don't think there is an issue with tapping the way you're showing provided you meet all the tap rule requirements.

  3. #3
    Join Date
    Feb 2003
    Location
    New York, 40.7514,-73.9925
    Posts
    4,471
    As mentioned, make sure you are keeping track of what is 700 and non-700 loads because they need to come from different take-offs.

    If you can move forward with the layout: You will have a challenge finding an ATS at that small size with a 42kA withstand on its own. You will likely need to change the 50A breaker to a fused switch as many ATS manufacturers will have a series rating for their smaller ATSs with current limiting fuses ie https://www.ascopower.com/globalasse...e-3-3-2017.pdf

    You can also consider recalculating the SCCR of the clinic ATS considering the impedance of the wire downstream of the 50A OCPD and the distance to the ATS, since it will knock down the fault current pretty fast.
    Ron

  4. #4
    Join Date
    May 2011
    Posts
    4,192
    As far as the tap itself, the tap conductor will probably have to be rated more than 50A per the 240.21(B) rules. The rule changes at 10ft, not 15ft, so it's unclear which section of the rule you'd be under; the drawing should probably specify not more than 10ft or 25ft, unless it's an outside tap.

    Other than getting the specifics right, and side issues others have mentioned, there's nothing wrong with the tap, conceptually.

  5. #5
    Join Date
    Feb 2003
    Location
    Pennsylvania
    Posts
    2,365
    Quote Originally Posted by anbm View Post
    The hospital and nearby clinic share same emergency generator.
    The inspector came out and want hospital and clinic must have
    their own ATS. Generator's 600A main breaker, 600A feeder, hospital's ATS-E2
    and downstream panels (cyan color) have been installed.

    The clinic and its panel (yellow color) will be installed. Does anyone see
    any code violation with this tap installation to new ATS-E1? ATS-E2 does
    not have a protection downstream of 600A CB.

    The total emergency load is less than 150kVA. Thanks!

    See attached picture.
    Thank you.


    SKE.pdfClick image for larger version. 

Name:	diagram.JPG 
Views:	32 
Size:	93.5 KB 
ID:	20510
    1 wounder why a 600 amp feed and over current protection for a load that is less than 450 amp max.

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