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Thread: 15 KVA ISOLATION TRANSFORMER GROUNDING

  1. #11
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    15 kva isolation transformer grounding

    I want to thank each and every person who has provided input on helping me find a solution to upload these images. I just need to figure out why the image is oriented correctly before upload, but then after upload it shows same image rotated 180 degrees. Thanks to all.

  2. #12
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    Ok so now that we have your images loaded we can answer your question.
    Click image for larger version. 

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    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #13
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    15 kva isolation transformer grounding

    Thank You for your help infinity. i,m assuming that you have seen the other image of the transformer spec sheet that is actually going to be installed. I posted my questions on the spec sheet as to make it easier as the questions were long. I have been told that I may need some sort of phase monitor with lamps that would show the first fault if that were to take place so I could find the fault and repair before a second fault appeared. i,m not sure if that applies to this situation.

  4. #14
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    15 kva isolation transformer grounding

    Hi to all. I,m posting my questions here as requested, as I have not received any responses to my questions posted in my sketch above. The one image shows the ACME spec sheet for the Xfmr that is actually being installed. It does not appear that the Xfmr is corner grounded. It appears that the Xfmr core is bonded to the case though. I'm assuming that the Xfmr case is grounded.

    Question#1- Can i run a #10 equipment ground from the 277/480 Panel that is feeding the primary of the Xfmr, and bond the Xfmr case, and continue that ground to the 240 volt, 3 phase panel and Bond that panel as well? The 240 volt, 3 phase panel is for two- 3 pole 20 amp breakers that are feeding 2- VFD,s. No neutrals being used.

    Question#2- Am I required to run a GEC from the Xfmr case to building steel? If so, can I run the GEC from the 240 volt, 3 phase panel to building steel instead?

    Question#3- would I need to install phase monitor lamps that would alert me that 1 of the phases have grounded, which would then allow me to repair the first fault before a second fault occurred, as the the first fault would not trip the OCPD?

    Question#4- Should I just bond the XO terminal of the Xfmr to the case instead of the above option, deriving the neutral and having a high leg at the 240 volt, 3 phase panel instead? This would seem to now require a bonding jumper and a supply side bonding jumper if I do it this way. I am hearing that this option may be safer.

    Thanks to all. I want to insure that I am installing this correctly.
    Last edited by tld38; 05-05-18 at 01:23 AM.

  5. #15
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    15 kva isolation transformer grounding

    I Was mistaken on last post. There is no XO terminal as this not a delta/wye Xfmr. According to the ACME Xfmr diagram, to establish the neutral, I would run a 4th wire from
    (X1,X4 Or X2, X4)? And this would create a high leg at the 240 volt/3 phase panel on B phase?

  6. #16
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    15 kva isolation transformer grounding

    Quote Originally Posted by infinity View Post
    Just snap a photo of the file and post it that way.
    uested, as I have not received any responses to my questions posted in my sketch above. The one image shows the ACME spec sheet for the Xfmr that is actually being installed. It does not appear that the Xfmr is corner grounded. It appears that the Xfmr core is bonded to the case though. I'm assuming that the Xfmr case is grounded.

    Question#1- Can i run a #10 equipment ground from the 277/480 Panel that is feeding the primary of the Xfmr, and bond the Xfmr case, and continue that ground to the 240 volt, 3 phase panel and Bond that panel as well? The 240 volt, 3 phase panel is for two- 3 pole 20 amp breakers that are feeding 2- VFD,s. No neutrals being used.

    Question#2- Am I required to run a GEC from the Xfmr case to building steel? If so, can I run the GEC from the 240 volt, 3 phase panel to building steel instead?

    Question#3- would I need to install phase monitor lamps that would alert me that 1 of the phases have grounded, which would then allow me to repair the first fault before a second fault occurred, as the the first fault would not trip the OCPD?

    Question#4- Should I just bond the XO terminal of the Xfmr to the case instead of the above option, deriving the neutral and having a high leg at the 240 volt, 3 phase panel instead? This would seem to now require a bonding jumper and a supply side bonding jumper if I do it this way. I am hearing that this option may be safer.

    Thanks to all. I want to insure that I am installing this correctly.
    Last edited by tld38; Today at 01:23 AM.

  7. #17
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    Quote Originally Posted by infinity View Post
    What kind of files are you trying to upload? Maybe you can provide a link instead of the files. I think that your Shift key is stuck.
    I Was mistaken on last post. There is no XO terminal as this not a delta/wye Xfmr. According to the ACME Xfmr diagram, to establish the neutral, I would run a 4th wire from
    (X1,X4 Or X2, X4)? And this would create a high leg at the 240 volt/3 phase panel on B phase?

  8. #18
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    Quote Originally Posted by tld38 View Post
    uested, as I have not received any responses to my questions posted in my sketch above. The one image shows the ACME spec sheet for the Xfmr that is actually being installed. It does not appear that the Xfmr is corner grounded. It appears that the Xfmr core is bonded to the case though. I'm assuming that the Xfmr case is grounded.

    Question#1- Can i run a #10 equipment ground from the 277/480 Panel that is feeding the primary of the Xfmr, and bond the Xfmr case, and continue that ground to the 240 volt, 3 phase panel and Bond that panel as well? The 240 volt, 3 phase panel is for two- 3 pole 20 amp breakers that are feeding 2- VFD,s. No neutrals being used.

    Question#2- Am I required to run a GEC from the Xfmr case to building steel? If so, can I run the GEC from the 240 volt, 3 phase panel to building steel instead?

    Question#3- would I need to install phase monitor lamps that would alert me that 1 of the phases have grounded, which would then allow me to repair the first fault before a second fault occurred, as the the first fault would not trip the OCPD?

    Question#4- Should I just bond the XO terminal of the Xfmr to the case instead of the above option, deriving the neutral and having a high leg at the 240 volt, 3 phase panel instead? This would seem to now require a bonding jumper and a supply side bonding jumper if I do it this way. I am hearing that this option may be safer.

    Thanks to all. I want to insure that I am installing this correctly.
    Last edited by tld38; Today at 01:23 AM.
    OK let's start with terminology for future reference. On the primary you have an EGC (Equipment Grounding Conductor) run with the circuit conductors. On the secondary you have a SSBJ (Supply Side Bonding Jumper) run with the derived or secondary conductors. From the midpoint of one winding on the secondary you have a GEC (Grounding Electrode Conductor) run to the GES (Grounding Electrode System), in this case building steel, and a SBJ (system bonding jumper) which connects the secondary midpoint to the SSBJ and EGC.

    1) Yes, if the EGC and SSBJ are the proper size.
    2) At 240/120 volts you have a midpoint on the secondary so you are required to connect a GEC to the GES. {250.20(B)(1)}.
    3) Not applicable because the secondary is required to be grounded, see #2.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  9. #19
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    15 kva isolation transformer grounding

    Infinity, thank you for your feedback. if you look at the 1st page of the thread, you will see the ACME drawing for the Xfmr I am going to install. It looks like the core is grounded to the case. I want to run the EGC from the 277/480 volt panel feeding the primary and bond to the Xfmr case. I will then run 3 hots with a SSBJ from the secondary to the 240 volt 3 phase panel. I will bond the SSBJ to the Xfmr case and the 240 volt 3 phase panel as well. I will bond the 240 volt 3 phase panel with the factory bonding screw or strap that is provided from the factory as well. I will then run a GEC from the Xfmr case to building steel. I do not need to derive a neutral from the separately derived system as there is no neutrals needed at the 240 volt 3 phase panel.


    Am I on the right path here? Thanks

  10. #20
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    You still need to connect S4 to the case (that is the supply side bonding jumper). This allows for fault current to return to the secondary coil.

    Your transformer output is a center tapped delta with a hi leg. Since your using it to power two VFD's, you might want to check the VFD manuals. Many of them are restricted from being powered from a hi leg delta. They often require a wye input or to disconnect the MOV input protection.

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