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Thread: transformer location ??

  1. #1
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    transformer location ??

    Hi ,
    i have to design a power distribution system to a new tenant moving , in an existing commercial space (a shell-designed space)
    all equipment in the new tenant space will be new.
    note that, the main 480/277v electrical switch gear in an dedicated -small electrical room is existing with spare tenant main OCPD.

    in order to step down that voltage to 120/208v, 3 ph. , i am using a step down transformer,

    QUESTION IS ,
    can install that transformer and its primary disconnect means inside the tenant space ?????
    I do not fully understand the tap rule



    Thank you

  2. #2
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    Quote Originally Posted by Toros View Post
    Hi ,
    i have to design a power distribution system to a new tenant moving , in an existing commercial space (a shell-designed space)
    all equipment in the new tenant space will be new.
    note that, the main 480/277v electrical switch gear in an dedicated -small electrical room is existing with spare tenant main OCPD.

    in order to step down that voltage to 120/208v, 3 ph. , i am using a step down transformer,

    QUESTION IS ,
    can install that transformer and its primary disconnect means inside the tenant space ?????
    I do not fully understand the tap rule



    Thank you
    A one line diagram of what you would like to do would be helpful.

  3. #3
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    How would the tap rule apply here?

    Don’t overlook the heat load and work space clearance issue in that room.
    __________________________________________________ ____________________________
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  4. #4
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    We install transformers in small electric closets all of the time. Its a standard installation practice in high rise buildings.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  5. #5
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    Quote Originally Posted by Toros View Post
    Hi ,
    i have to design a power distribution system to a new tenant moving , in an existing commercial space (a shell-designed space)
    all equipment in the new tenant space will be new.
    note that, the main 480/277v electrical switch gear in an dedicated -small electrical room is existing with spare tenant main OCPD.

    in order to step down that voltage to 120/208v, 3 ph. , i am using a step down transformer,

    QUESTION IS ,
    can install that transformer and its primary disconnect means inside the tenant space ?????
    I do not fully understand the tap rule



    Thank you
    In the simplest terms, the tap rule breaks down unprotected feeders tapped from protected conductors into 5 categories (and more if from a transformer secondary:
    1. Not over 10 ft long
    2. Between 10 ft at 25 ft
    3. Supplying a transformer), not over 25 ft
    4. Over 25 ft
    5. Outside unlimited length


    It's isn't clear to me that any of these apply to your installation because you are obtaining power from a spare OCPD in a switchboard. A example of the tap rule is if you were to take an existing #3 AWG circuit protected by a 100 A breaker and tap #8's from it. Those #8's are not protected by the breaker. This is permitted provided compliance with the provisions set forth in 240.21 (the tap rule).

    Installing the equipment in the tenant space is a matter of designer/tenant preference.

  6. #6
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    If this is a tenant build out in a commercial space, there is certainly an architect involved. Where do they want it? Their layout of the space usually dictates rooms.
    "Just because you're paranoid, doesn't mean they're not out to get you"

  7. #7
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    Quote Originally Posted by Jraef View Post

    Don’t overlook the heat load and work space clearance issue in that room.
    Very good points if I may say so...
    I'm sure we've all seen installations where insufficient consideration has been given to these fundamental issues.
    Si hoc legere scis nimium eruditionis habes.

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