Page 1 of 3 123 LastLast
Results 1 to 13 of 28
  1. #1
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,764

    Ungrounded 480 delta anomaly.

    I've worked with ungrounded delta systems for years at multiple locations, and haven't seen this one.

    An ungrounded 480 delta system, with about 280 volts to ground on all three legs.

    I know for a fact it is an ungrounded system, even looked inside the secondary side of the trans.

    A 24/7 plant, where I can't just start shutting down things to see what makes the voltage to ground go away.
    No ground indicator lights, or any electronic ground detection at all.

    I informed the on site electrician that there is some kind of problem needing to be addressed.

    Am I losing my mind here?
    God Bless the USA

  2. #2
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,035
    It's hard to imagine that they would want to be running an ungrounded Delta 480-volt without ground detectors. That seems crazy to me.

    I would want to isolate a transformer and get out the Megger and see if there's a leak somewhere.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  3. #3
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,925
    "IF" you had a phase shorted to ground somewhere , logically the numbers would come out more like a grounded delta system. But the whole point of an ungrounded delta system is to not go to ground and take out the system.
    The fact that you have the same voltage to ground on all three phases says to me that somebody , somewhere created a neutral. A 480 wye transformer, perhaps for 277 loads.

  4. #4
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,867

  5. #5
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,035
    Quote Originally Posted by Core_d View Post
    This should have been flagged by the guy who put his stamp on the print. In an environment that is exposed to the public, you should not be using a multiphase ungrounded system, for the reasons given. A ground detector setup is there so that in a plant, you can repair the ground BEFORE you get a second grounded phase, which stops everything.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  6. #6
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,867
    Quote Originally Posted by timebuilder View Post
    This should have been flagged by the guy who put his stamp on the print. In an environment that is exposed to the public, you should not be using a multiphase ungrounded system, for the reasons given. A ground detector setup is there so that in a plant, you can repair the ground BEFORE you get a second grounded phase, which stops everything.
    So why is he reading voltage to ground? In the article he says he intentionally grounded a leg and nothing happened?

  7. #7
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,867
    Ive often wandered this. Ive tested ungrounded 120/24v transformers to ground and get lets say 15v one led and 8v one leg yet, wont short to ground?

  8. #8
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,035
    Quote Originally Posted by Core_d View Post
    So why is he reading voltage to ground? In the article he says he intentionally grounded a leg and nothing happened?

    Because nothing happens if only one leg is grounded.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  9. #9
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,035
    Quote Originally Posted by Core_d View Post
    Ive often wandered this. Ive tested ungrounded 120/24v transformers to ground and get lets say 15v one led and 8v one leg yet, wont short to ground?
    Leakage.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  10. #10
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,867
    Quote Originally Posted by timebuilder View Post
    Because nothing happens if only one leg is grounded.
    If one leg was "grounded" to start with on an ungrounded system you would only read potential across the other two legs to ground. Correct?

  11. #11
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,867
    Another good thread on the subject. http://www.electrical-contractor.net...ded_Delta.html. Try testing with an analog meter or putting a load to ground you'll probably get nothing.

  12. #12
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,764
    I neglected to mention that the voltage to ground I observed was with both a DMM and a Wiggy type tester.
    So, it's not just "stray" voltage. No 277 loads in the plant, that I know of, anyhow.
    Suspected a TVSS device and isolated it, with no change.

    And yes it makes me think that there's some transformer for 277, but I didn't see anything like that.
    I'll prowl through the whole place next time I'm there.

    If I come up with an answer, I'll be sure to post it here.
    God Bless the USA

  13. #13
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    1,867
    Quote Originally Posted by Randy S. View Post
    I neglected to mention that the voltage to ground I observed was with both a DMM and a Wiggy type tester.
    So, it's not just "stray" voltage. No 277 loads in the plant, that I know of, anyhow.
    Suspected a TVSS device and isolated it, with no change.

    And yes it makes me think that there's some transformer for 277, but I didn't see anything like that.
    I'll prowl through the whole place next time I'm there.

    If I come up with an answer, I'll be sure to post it here.
    For fun post a video of lighting a light bulb from the floor. Im assuming you have some type of conductive floor. If that don't get attention I don't know what will.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event