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Thread: Tap at 750kVA unit substation switchgear section

  1. #1
    Join Date
    Oct 2004
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    Forth Worth, TX
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    Tap at 750kVA unit substation switchgear section

    At an existing indoor 750kVA 4160/480v unit substation that has two breaker feeders in the switchgear section. The transformer primary OCPD fuse is 100E. There is no space available to add another feeder breaker. The design calls for connecting 2x3(700mcm) cables at the switchgear bus and run that over to 1000 amp Frame/900 amp trip wall mounted breaker disconnect OCPD. The total run is less than 25 feet at an adjacent wall. Can I please get a double check that I met requirements of 240.21(B)(2) taps not over 25 feet long. Is thee any other considerations? thanks

  2. #2
    Join Date
    Aug 2004
    Location
    Northern illinois
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    Other considerations:

    How do you plan to shut down the plant to tap the bus?

    How do you plan to tap the bus? Is the switchgear manufacturer providing some kind of kit, or at least his blessing on how you are doing it?
    Bob

  3. #3
    Join Date
    Feb 2003
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    Seattle, WA
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    18,427
    Quote Originally Posted by dwinchel View Post
    Can I please get a double check that I met requirements of 240.21(B)(2) taps not over 25 feet long. Is thee any other considerations? thanks
    I think not. It sounds like the design is calling for a tap on the switchgear buswork. If there is no overcurrent device upstream of that point (i.e., a main between the transformer secondary and the two feeder breakers), then 240.21(B) does not apply. You would be tapping the transformer secondary, and the rules in 240.21(C) come into play. If the distance were under 10 feet, I think you could use (C)(2). Otherwise, try (C)(6).

    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

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