User Tag List

Page 1 of 3 123 LastLast
Results 1 to 10 of 25

Thread: Transformer not used to capacity

  1. #1
    Join Date
    Jul 2007
    Location
    Utah
    Posts
    18
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Transformer not used to capacity

    Name:  nameplate.jpg
Views: 550
Size:  6.1 KB

    This is the nameplate of a transformer that is to feed a piece of equipment. The secondary feeder will land on a 160 amp breaker that feeds the equipment. The engineer that has designed the install, has sized the transformer to its max capacity and is requiring feeders much larger than 160 amp. I physically do not have enough space to do this however; he insists that the conductors must be sized to the nameplate of the transformer. Call me crazy, but there is nothing that requires me to use 100% of the transformer and I should be able to size my secondary conductors off of the 160 amp breaker, correct? no other loads will be fed by this transformer. He is also insisting that the primary conductors would be sized for 270 amps which is 125% of the nameplate. But again, if Im not using the transformer to its capacity, am I required to have OCPD and conductors sized to the nameplate?

  2. #2
    Join Date
    Jul 2007
    Location
    Utah
    Posts
    18
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I just realized that is a horrible picture. It is a german Transformer 480V primary 400 V secondary. 180/185 KVA. Pri I 230A. Sec I 267A.
    Schaltung Ya0. I dont know what Shaltung Ya0 is but the engineer is also insisting that the primary and secondary require a nuetral. I have no where to land nuetrals in the transformer or the equipment. He is saying that it is a YY transformer.

  3. #3
    Join Date
    Aug 2004
    Location
    Northern illinois
    Posts
    16,996
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by nathanslc View Post
    I just realized that is a horrible picture. It is a german Transformer 480V primary 400 V secondary. 180/185 KVA. Pri I 230A. Sec I 267A.
    Schaltung Ya0. I dont know what Shaltung Ya0 is but the engineer is also insisting that the primary and secondary require a nuetral. I have no where to land nuetrals in the transformer or the equipment. He is saying that it is a YY transformer.
    if it is german it probably is Y-Y.

    It likely does not need a neutral coming in but the secondary probably does need to have a neutral that is grounded.

    I don't recall off the top of my head for sure, but I think the language of the code requires one to have both primary conductor protection and primary transformer protection. I don't recall there is a minimum ampacity for the conductors or a minimum rating for the OCPD on the primary.

    OTOH, if the engineer wants it done this way, maybe he knows something about future needs you don't or just wants it done that way. It is his call to make.
    Bob

  4. #4
    Join Date
    Jul 2007
    Location
    Utah
    Posts
    18
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by petersonra View Post
    if it is german it probably is Y-Y.

    It likely does not need a neutral coming in but the secondary probably does need to have a neutral that is grounded.

    I don't recall off the top of my head for sure, but I think the language of the code requires one to have both primary conductor protection and primary transformer protection. I don't recall there is a minimum ampacity for the conductors or a minimum rating for the OCPD on the primary.

    OTOH, if the engineer wants it done this way, maybe he knows something about future needs you don't or just wants it done that way. It is his call to make.
    Normally I would agree and just do it. In this case, I physically cannot install how it was designed. The end user just wants the equipment to run the way it was.

  5. #5
    Join Date
    Jun 2014
    Location
    Madison, WI, USA
    Posts
    355
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by nathanslc View Post
    Normally I would agree and just do it. In this case, I physically cannot install how it was designed. The end user just wants the equipment to run the way it was.
    You do not have to size the wiring to the maximum capacity of the Transformer. You size the wiring according to the ocpd and load requirements

    Sent from my A574BL using Tapatalk
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  6. #6
    Join Date
    Jun 2014
    Location
    Madison, WI, USA
    Posts
    355
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Just always remember this rule of thumb. Everything we do as far as service and feeder calculations as well as branch circuit selection has to do with the total connected load

    Sent from my A574BL using Tapatalk
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  7. #7
    Join Date
    Jul 2007
    Location
    Utah
    Posts
    18
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by DrSparks View Post
    Just always remember this rule of thumb. Everything we do as far as service and feeder calculations as well as branch circuit selection has to do with the total connected load

    Sent from my A574BL using Tapatalk
    Thanks for the reply! So in this case, my OCPD on my secondary will be 160A and I can size my wiring on that. Working backwards from secondary to primary, would I then use a voltage ratio to get my primary OCPD and feeder sizes?

  8. #8
    Join Date
    Jun 2014
    Location
    Madison, WI, USA
    Posts
    355
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by nathanslc View Post
    Thanks for the reply! So in this case, my OCPD on my secondary will be 160A and I can size my wiring on that. Working backwards from secondary to primary, would I then use a voltage ratio to get my primary OCPD and feeder sizes?
    Yup but remember you can round up to the next higher standard ocpd rating if under 800a

    Sent from my A574BL using Tapatalk
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  9. #9
    Join Date
    May 2007
    Location
    Westminster, MD
    Posts
    632
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by nathanslc View Post
    Thanks for the reply! So in this case, my OCPD on my secondary will be 160A and I can size my wiring on that. Working backwards from secondary to primary, would I then use a voltage ratio to get my primary OCPD and feeder sizes?
    You could have a problem with an energization trip if you size that primary breaker to just meet the dedicated load. But, in order to increase the breaker size you'll have to increase the size of the wire. 450.3(B) gives you as much as 250% for inrush tolerance.
    Perhaps bench test the energization before wiring it permanent.

  10. #10
    Join Date
    Jun 2014
    Location
    Madison, WI, USA
    Posts
    355
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by mayanees View Post
    You could have a problem with an energization trip if you size that primary breaker to just meet the dedicated load. But, in order to increase the breaker size you'll have to increase the size of the wire. 450.3(B) gives you as much as 250% for inrush tolerance.
    Perhaps bench test the energization before wiring it permanent.
    Standard inverse time curve should allow for inrush current

    Sent from my A574BL using Tapatalk
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

Posting Permissions

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