Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: How to tie in neutral bar

  1. #1
    Join Date
    May 2017
    Location
    Lexington, Kentucky, United States
    Posts
    1

    How to tie in neutral bar

    We have just installed 3 new pad mount 12470 Delta / 480 Wye transformers. We have no neutral load, it's all 3 phase motors. I have a ground grid we just installed, how should that tie into my transformer and should anything be tied to the neutral bar in the low side of my transformer? Right now it goes to the ground spot on the transformer and then to the first disconnect, but it seems like there is no way for any fault current to get back to the transformer.

  2. #2
    Join Date
    Feb 2009
    Location
    Durango, CO, 10 h 20 min without traffic from winged horses.
    Posts
    8,756
    250.30, you either bond the XO and earth it in the transformer or in the first disconnect, either or, not both.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  3. #3
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,385
    This is not a service transformer?

    Do you want a grounded system? In heavy industry it is common to run systems ungrounded, especially where a trip can present a more dangerous condition than a line to ground fault. After all, one line to ground fault on an ungrounded system is not much different than the intentional ground of a grounded system. A ground detector is required, along with it being monitored and faults corrected as soon as can be safely managed.

    If you want a grounded system, Dave has directed you to the appropriate section (if not a service transformer). There are a lot of details to that section so it is difficult to cover all the possible specifics here. So read up if that's the route you want to go, and come back if you have any additional questions.

    Welcome to the forum.
    I will have achieved my life's goal if I die with a smile on my face.

  4. #4
    Join Date
    Apr 2016
    Location
    Raleigh, NC USA
    Posts
    350
    This graphic may be helpful
    Attached Images Attached Images  

  5. #5
    Join Date
    Jan 2014
    Location
    chicago, il, USA
    Posts
    340
    I'm only asking this as I'm curious, I understand that it isn't practical to change anything now. Wouldn't it have been better to use a Delta secondary since there are exclusively motor loads? If so, then you could corner ground the Delta secondary.

    I'm hopeful that some of the other members can weigh in on this as I would like to know what is considered the convention way of doing it.
    The world is round, you will get there no matter what path you take.

  6. #6
    Join Date
    Feb 2009
    Location
    Durango, CO, 10 h 20 min without traffic from winged horses.
    Posts
    8,756
    Quote Originally Posted by Smart $ View Post
    This is not a service transformer?...
    His handle says Mine electrician. I would not be surprised that those are their own transformers.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  7. #7
    Join Date
    Feb 2009
    Location
    Durango, CO, 10 h 20 min without traffic from winged horses.
    Posts
    8,756
    Quote Originally Posted by rlundsrud View Post
    I'm only asking this as I'm curious, I understand that it isn't practical to change anything now. Wouldn't it have been better to use a Delta secondary since there are exclusively motor loads? If so, then you could corner ground the Delta secondary.

    I'm hopeful that some of the other members can weigh in on this as I would like to know what is considered the convention way of doing it.
    Wye systems are more familiar and have the added advantage of reducing the voltage to ground.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  8. #8
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,385
    Quote Originally Posted by ActionDave View Post
    His handle says Mine electrician. I would not be surprised that those are their own transformers.
    I would not be surprised either. But I had to ask because the grounding details are a little different (as is the section that covers such).
    I will have achieved my life's goal if I die with a smile on my face.

  9. #9
    Join Date
    Nov 2010
    Location
    Fort Collins, Colorado
    Posts
    2,435
    Quote Originally Posted by rlundsrud View Post
    I'm only asking this as I'm curious, I understand that it isn't practical to change anything now. Wouldn't it have been better to use a Delta secondary since there are exclusively motor loads? If so, then you could corner ground the Delta secondary.

    I'm hopeful that some of the other members can weigh in on this as I would like to know what is considered the convention way of doing it.
    There are a number of reasons why a Y system would be better than a delta (even when there are only line to line loads). Among them, the phase to ground voltage is the same as line to line in a corner grounded system and thus requires equipment rated for this. In this day and age, corner grounded delta rated equipment such as panelboards, etc. is becoming less common. Also much load equipment these days, such as VFDs are not suitable for use in a corner grounded systems.

  10. #10
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    18,374
    Quote Originally Posted by texie View Post
    There are a number of reasons why a Y system would be better than a delta (even when there are only line to line loads). Among them, the phase to ground voltage is the same as line to line in a corner grounded system and thus requires equipment rated for this. In this day and age, corner grounded delta rated equipment such as panelboards, etc. is becoming less common. Also much load equipment these days, such as VFDs are not suitable for use in a corner grounded systems.
    The NEC also specifically instructs us to consider the effective phase to ground voltage in an ungrounded system to be equal to the line to line voltage. That will also affect what equipment you can use.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •