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Thread: No primary protection required?

  1. #1
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    No primary protection required?

    Contractor wants to put two, single phase 3kVA transformers in line to boost the voltage up then bring it down at the load (120/480V to 480/120V) due to V-drop at 1700+ feet from source. Cable between transformers is 2#6 AWG w/#8 Gnd.There is no primary protection on the second transformer. This seems to be a violation of450.3(B). Contractor says "No" since fault current between the two Xfmrs is not sufficient to cause damage. I don’t see any exceptions that would allow this. Comments?

  2. #2
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    The secondary of the second transformer would be grounded but the wiring between the first transformer and the second transformer would usually be balanced, as I understand such uses. Thus no extra protection would be needed there. Or at least that is what I have been understanding , though I have never done such a set up.
    Student of electrical codes. Please Take others advice first.

  3. #3
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    Quote Originally Posted by Adamjamma View Post
    The secondary of the second transformer would be grounded but the wiring between the first transformer and the second transformer would usually be balanced, as I understand such uses. Thus no extra protection would be needed there. Or at least that is what I have been understanding , though I have never done such a set up.

    If a ground fault occurred between the two xfmrs how would it be cleared if there is no overcurrent device? The primary device, i.e. CB on the first transformer would not see the fault.

  4. #4
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    The second transformer needs an OCPD.
    Last edited by jumper; 10-06-18 at 09:21 AM.
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #5
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    If both are two wire in / two wire out, I think one OCPD in the supply can protect everything. Had the load end been 120/240 on secondary then it would have needed protection on it's secondary side.
    I live for today, I'm just a day behind.

  6. #6
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    Quote Originally Posted by kwired View Post
    If both are two wire in / two wire out, I think one OCPD in the supply can protect everything. Had the load end been 120/240 on secondary then it would have needed protection on it's secondary side.
    I do not know of any exceptions to omit primary protection on the second tranny.

    Second tranny also needs a disconnecting means, 450.14.
    "Electricity is really just organized lightning." George Carlin


    Derek

  7. #7
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    Quote Originally Posted by jumper View Post
    I do not know of any exceptions to omit primary protection on the second tranny.

    Second tranny also needs a disconnecting means, 450.14.

    Agreed.

  8. #8
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    Quote Originally Posted by Isaiah View Post
    If a ground fault occurred between the two xfmrs how would it be cleared if there is no overcurrent device? The primary device, i.e. CB on the first transformer would not see the fault.
    For this install I believe that 240.4(F) allows the primary protection for the first tranny to protect the primary and secondary of the tranny and secondary conductors also.
    "Electricity is really just organized lightning." George Carlin


    Derek

  9. #9
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    Quote Originally Posted by jumper View Post
    For this install I believe that 240.4(F) allows the primary protection for the first tranny to protect the primary and secondary of the tranny and secondary conductors also.

    I'm more concerned about the primary windings of the second tranny.

  10. #10
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    Quote Originally Posted by Isaiah View Post
    I'm more concerned about the primary windings of the second tranny.
    Well, when the electrician installs the required disco and OCPD, yout concerns will be gone.

    Besides that, I am not 100% sure about the first tranny OCPD protecting the conductors so landing them in an OCPD is a good idea.
    "Electricity is really just organized lightning." George Carlin


    Derek

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