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Thread: Generators as prime power

  1. #1
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    Generators as prime power

    I'm hoping to find some guidance regarding generators. Most everything I can find regarding generators deals with portable or back up but I'm working overseas in an environment where they are essentially prime power. I've tried to research this but honestly the more I dive into it the more I confuse myself. I'm hoping some of you can provide me with some clarity.

    I'll give a direct example and then extrapolate out from there. There is a 120 kW generator being brought on line. There is a neutral to ground bond in the gen. it will feed out via G cable and a pin and sleeve connector to essentially a spider box. Out of that spider box are more pin and sleeve connectors and more G cable going out to the various loads.

    The simple question is this: does this generator need a ground rod? (For what it's worth the gen will not actually be in touch with the earth- it sits on 4x4s inside a containment bladder to catch fuel spills.) I've read that it does, I've read that it does not. The way that I'm looking at this is that I'm not sure what the ground rod will add. But I've been known to be wrong before.

    Any opinions you have would be appreciated (well, opinions about the grounding thing- if you're opinion is that I'm funny looking and listen to bad music, well those wouldn't be appreciated...)
    "If you don't do it this year , you'll be one year older when you do" Warren Miller

  2. #2
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    Quote Originally Posted by ishium 80439 View Post
    I'm hoping to find some guidance regarding generators. Most everything I can find regarding generators deals with portable or back up but I'm working overseas in an environment where they are essentially prime power. I've tried to research this but honestly the more I dive into it the more I confuse myself. I'm hoping some of you can provide me with some clarity.

    I'll give a direct example and then extrapolate out from there. There is a 120 kW generator being brought on line. There is a neutral to ground bond in the gen. it will feed out via G cable and a pin and sleeve connector to essentially a spider box. Out of that spider box are more pin and sleeve connectors and more G cable going out to the various loads.

    The simple question is this: does this generator need a ground rod? (For what it's worth the gen will not actually be in touch with the earth- it sits on 4x4s inside a containment bladder to catch fuel spills.) I've read that it does, I've read that it does not. The way that I'm looking at this is that I'm not sure what the ground rod will add. But I've been known to be wrong before.

    Any opinions you have would be appreciated (well, opinions about the grounding thing- if you're opinion is that I'm funny looking and listen to bad music, well those wouldn't be appreciated...)
    The generator itself probably doesn't need a ground rod.

    The wiring system you connect it to likely does need a grounding electrode system though.
    I live for today, I'm just a day behind.

  3. #3
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    That is what I'm trying to understand. What these G cables are feeding are mostly tents with a pre-packaged wiring system- plug and play if you will. There is no concrete, there is no piping, there is no structural steel.

    I took a grounding and bonding class with Mr. Holt about a year ago and I unfortunately left my notes and his book back home. What I do remember from that class was that ground rods were really over hyped and essentially provided some marginal level of lightning protection. There was a bit more to it but that is what I remember it boiling down to.

    So in this situation what purpose would a ground rod serve? If one is needed where would you put it? At the first spider box? To reiterate the more I try to reason this out the more I confuse myself....
    "If you don't do it this year , you'll be one year older when you do" Warren Miller

  4. #4
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    i found this in 250>


    (2) Grounding Electrode. Except as permitted by 250.34 for
    portable and vehicle-mounted generators, the grounding elec‐
    trode shall comply with 250.30(A)(4).

    ~RJ~

  5. #5
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    Quote Originally Posted by romex jockey View Post
    i found this in 250>

    (2) Grounding Electrode. Except as permitted by 250.34 for
    portable and vehicle-mounted generators, the grounding elec‐
    trode shall comply with 250.30(A)(4).


    ~RJ~
    If that is 250.30(B)(2), which I think it is, (B) is titled "ungrounded systems"

    But then it is sending you to a section in (A) "grounded systems" so I guess it applies whether a grounded system or not.
    I live for today, I'm just a day behind.

  6. #6
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    Thx Kwired

    I'm confused

    what's the theory here? do we protect the structure,or the power source from mother nature, or both?

    ~RJ~

  7. #7
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    Quote Originally Posted by romex jockey View Post
    Thx Kwired

    I'm confused

    what's the theory here? do we protect the structure,or the power source from mother nature, or both?

    ~RJ~
    We install a grounding electrode - unless it is portable or vehicle mounted generator.

    Now if you are supplying fixed premises wiring you need a GES at each structure no matter what the source is, even if it is an ungrounded system.
    I live for today, I'm just a day behind.

  8. #8
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    Thanks for the responses. Forgive me if this is an ignorant question but I'm really trying to understand this. What role does the ground rod serve in this installation? What is the role of the grounding electrode here?
    "If you don't do it this year , you'll be one year older when you do" Warren Miller

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