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Thread: 4160 Delta Secondary Grounded or Ungrounded

  1. #11
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    In years gone past, I used to recommend that delta secondaries be ungrounded when they feed a single circuit and corner-grounded when they feed multiple circuits.

    What are you planning to do for a ground detection scheme? Will you have any protective relaying on the 4160V?
    Just because you can, doesn't mean you should.

  2. #12
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    Quote Originally Posted by jim dungar View Post
    In years gone past, I used to recommend that delta secondaries be ungrounded when they feed a single circuit and corner-grounded when they feed multiple circuits.

    What are you planning to do for a ground detection scheme? Will you have any protective relaying on the 4160V?
    The 4160 secondary feeds a fused disconnect and as far as I can see that's it. Is ground detection required?
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #13
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    Quote Originally Posted by infinity View Post
    The 4160 secondary feeds a fused disconnect and as far as I can see that's it. Is ground detection required?
    250.21(B) only requires ground detection for systems operating at 1000 volts or less. I don't see anything in Part X of 250 requiring ground detection for the higher voltage systems.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  4. #14
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    Quote Originally Posted by don_resqcapt19 View Post
    250.21(B) only requires ground detection for systems operating at 1000 volts or less. I don't see anything in Part X of 250 requiring ground detection for the higher voltage systems.
    That's what I thought as well, seems to be a design issue not a code issue
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  5. #15
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    Quote Originally Posted by infinity View Post
    That's what I thought as well, seems to be a design issue not a code issue
    You are correct, this is a design choice.

    One I did like this was for a Scout camp, the MV was run through the woods (buried) and across a river. With all of the 'critters' out there we were concerned a ground fault would not be noticed until it was catastrophic.
    Just because you can, doesn't mean you should.

  6. #16
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    This came up the other day because someone asked me about running GEC's for these step-up transformers. When I took a closer look at the set up I realized that this was designed as an ungrounded system which yielded some strange looks. Sometimes electricians cannot understand how a system could be installed that is not grounded especially at 4160 volts.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  7. #17
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    Quote Originally Posted by infinity View Post
    .... Sometimes electricians cannot understand how a system could be installed that is not grounded especially at 4160 volts.
    How does it work without a ground? has to be in the top five questions of all time. I can understand common folk asking that, but electricians should know better.
    If you don't think too good, don't think too much.

  8. #18
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    Quote Originally Posted by infinity View Post
    This came up the other day because someone asked me about running GEC's for these step-up transformers. When I took a closer look at the set up I realized that this was designed as an ungrounded system which yielded some strange looks. Sometimes electricians cannot understand how a system could be installed that is not grounded especially at 4160 volts.
    Even though you arent grounding a conductor of the system, Dont you still need a GEC for the metal parts?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  9. #19
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    Quote Originally Posted by electrofelon View Post
    Even though you arent grounding a conductor of the system, Dont you still need a GEC for the metal parts?
    For the step-ups the metal parts are connected to the EGC in the feeder which is anywhere from 5-8 sets of 4" EMT feeding the 208 volt primary. I would guess that if one phase of the 4160 were to fault to ground the system would still operated as a corner grounded system. For the step-downs the 208Y/120 secondary would be wired like a typical transformer with a EGC, GEC, SBJ and SSBJ.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  10. #20
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    Quote Originally Posted by infinity View Post
    This came up the other day because someone asked me about running GEC's for these step-up transformers. When I took a closer look at the set up I realized that this was designed as an ungrounded system which yielded some strange looks. Sometimes electricians cannot understand how a system could be installed that is not grounded especially at 4160 volts.
    I think the grounding electrode system and GECs are required. The only real difference between the rules for a grounded and ungrounded transformer is that the ungrounded one does not have a system bonding jumper.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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