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Thread: Transformer grounding

  1. #1
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    Transformer grounding

    Attached is power riser and transformer grounding detail. The transformer grounding detail belongs to transformer T labeled #6 on power riser uses building steel and main service ground bar. NEC 2014 Article 250, Section 250.30(A)(4) says to have grounding electrode as metal water pipe or structural metal as grounding electrode. Exception No. 2 says grounding electrode used for the service or feeder equipment shall be permitted if originates in listed equipment. Attach picture transformer is 120 feet from switchboard. My question is transformer grounding detail is it per NEC 2014 Article 250.30(A)(4)?
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  2. #2
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    The GEC only needs to go to the building steel.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    Quote Originally Posted by infinity View Post
    The GEC only needs to go to the building steel.
    Problem is this is existing building not new. So not sure if building steel is actually electode or not. There are certain perimeters for bldg steel to be electrode i forget whcih code section Article 250. The underground water pipe is not reliable electrode. What to do in that case?

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  4. #4
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    If it's not an electrode then no sense connecting to it. Also under the 2017 you need a terminal bar connected to the case of the XFMR.

    450.10 Grounding.(A) Dry-Type Transformer Enclosures. Where separate equip‐ment grounding conductors and supply-side bonding jumpersare installed, a terminal bar for all grounding and bondingconductor connections shall be secured inside the transformerenclosure. The terminal bar shall be bonded to the enclosurein accordance with 250.12 and shall not be installed on or overany vented portion of the enclosure.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  5. #5
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    Quote Originally Posted by infinity View Post
    If it's not an electrode then no sense connecting to it. Also under the 2017 you need a terminal bar connected to the case of the XFMR.
    We are still in 2014. But i am not sure if steel is electrode in this building and underground water pipe is not reliable. What else I can do per nec 2014?

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  6. #6
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    Quote Originally Posted by codequestion View Post
    We are still in 2014. But i am not sure if steel is electrode in this building and underground water pipe is not reliable. What else I can do per nec 2014?
    Read the exceptions to 250.30(A)(4)

    Roger
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  7. #7
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    Quote Originally Posted by codequestion View Post
    Attached is power riser and transformer grounding detail. The transformer grounding detail belongs to transformer T labeled #6 on power riser uses building steel and main service ground bar. NEC 2014 Article 250, Section 250.30(A)(4) says to have grounding electrode as metal water pipe or structural metal as grounding electrode. Exception No. 2 says grounding electrode used for the service or feeder equipment shall be permitted if originates in listed equipment. Attach picture transformer is 120 feet from switchboard. My question is transformer grounding detail is it per NEC 2014 Article 250.30(A)(4)?
    I have another question transformer gnd detail. Primary equipment ground is connected to the bar in transformer which is connected to the secondary equipment ground cable. Nec 2014 handbook echibit 250.14 shows connection the primary at transformer enclosure. Would the attached grounding detail still compliance per NEC 2014 250.30 in regards to equipment ground connections shown origonal poster?

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  8. #8
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    Quote Originally Posted by codequestion View Post
    I have another question transformer gnd detail. Primary equipment ground is connected to the bar in transformer which is connected to the secondary equipment ground cable. Nec 2014 handbook echibit 250.14 shows connection the primary at transformer enclosure. Would the attached grounding detail still compliance per NEC 2014 250.30 in regards to equipment ground connections shown origonal poster?

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    There should be an equipment ground from both the primary and secondary tied to the transformer case. The drawing looks correct.
    If Billy Idol or John Denver is on your play list go and reevaluate your life.

  9. #9
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    Bonding

    Doesn't matter if the building steel is not used as and electrode, you still have to bond it....said every inspector ever....... Hit the transformer then steel.. I just had to bond a structural beam holding up wood beams for a stick built building in Oregon. (Just one pillar) Also sized for the service. I argued it was ridiculous but 90.4 overruled...and my shop said just do it.

  10. #10
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    Quote Originally Posted by Sparky1999 View Post
    I just had to bond a structural beam holding up wood beams for a stick built building in Oregon. (Just one pillar) Also sized for the service. I argued it was ridiculous but 90.4 overruled...and my shop said just do it.
    There's what's required by the NEC and what's required by someone is making up their own code. Your example is the latter.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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