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Thread: Grounded (Neutral) Conductor Sizing NEC 220.61

  1. #1
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    Grounded (Neutral) Conductor Sizing NEC 220.61

    What's the consensus. If ungrounded conductors are increased in size due to voltage drop concerns, is the neutral or grounded conductor also increased?

    I know the equipment ground must be upsized per NEC 250.122(B). I'm thinking the answer is yeas based on 240.23. Although the term "shall be permitted" rather than must be, or is required has got me thinking.

    Thoughts and input are greatly appreciated.

  2. #2
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    Quote Originally Posted by cdcengineer View Post
    What's the consensus. If ungrounded conductors are increased in size due to voltage drop concerns, is the neutral or grounded conductor also increased?

    I know the equipment ground must be upsized per NEC 250.122(B). I'm thinking the answer is yeas based on 240.23. Although the term "shall be permitted" rather than must be, or is required has got me thinking.

    Thoughts and input are greatly appreciated.
    The grounded conductor would only need to be upsized if it is required for VD or other reasons. The grounded conductor, however, cannot be smaller than the egc.

  3. #3
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    Voltage Drop shouldn't be an issue with the neutral unless it's a current carrying conductor (as might be the case with certain types of lighting, etc.). No?

    So the neutral is not automatically upsized to match the feeders when the feeders are upsized due to voltage drop?

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    If this is a feeder, take a look at 215.2(A)(1) in the 2008 code.
    215.2(A)(1) ... The size of the feeder circuit grounded conductor shall not be smaller than that required by 250.122, except that 250.122(F) shall not apply where grounded conductors are run in parallel. ...
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  5. #5
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    Quote Originally Posted by cdcengineer View Post
    Voltage Drop shouldn't be an issue with the neutral unless it's a current carrying conductor (as might be the case with certain types of lighting, etc.). No?

    So the neutral is not automatically upsized to match the feeders when the feeders are upsized due to voltage drop?
    I would agree in that scenario. In some cases the neutral is only needed for a 120v control circuit. In that case the neutral still cannot be smaller than the egc. Don gave the article I neglected to cite.

  6. #6
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    Thanks to you both..

    Our scenario is this:

    We have a 400Amp, 208Y/120V handle in the MDS which is serving a branch circuit panelboard (84 circuit, rated 400Amps) with 350kcmil AL THW feeders with a 250kcmil neutral. The EGC has been upsized with the ungrounded feeders. The actual length is roughly 275', and the calculated load is roughly 320Amps.

    My voltage drop calculation (@3%) at the max panel rating (400Amps) allows a run of roughly 290' with 350kcmil AL, at 325Amps (the calculated load), the 250kcmil AL would be good for roughly 260'. So I'm not sure why the neutral was ever down-sized in the 1st place?

    Now bear in mind that these are existing conditions... If new, I wouldn't size a neutral smaller than the ungrounded conductors unless I could do so based on 220.61, however, the ownership wants to keep these feeders unless it's absolutely necessary to change them.

    I think we're good with the 250kcmil neutral.

    Thanks

  7. #7
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    Bump

    So to ask again, if I upsize feeders due to voltage drop concerns, do I have to upsize the neutral? I know we upsize the equipment grounding conductor.

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    I am still not sure what your calculated neutral load is?

  9. #9
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    It's hard to say. There are a ton of lights, general use receptacles and small pumps and motors.

    If I had to estimate, the total load on the panel is 350 Amps (125kVA). Of that, I would estimate that 90kVA is 120V load. Hard to say what the neutral might see.

    Am I looking at this right?

  10. #10
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    Quote Originally Posted by cdcengineer View Post
    It's hard to say. There are a ton of lights, general use receptacles and small pumps and motors.

    If I had to estimate, the total load on the panel is 350 Amps (125kVA). Of that, I would estimate that 90kVA is 120V load. Hard to say what the neutral might see.

    Am I looking at this right?
    Yes... but your neutral load is dependent on balance. If balanced, it would be 90kVA รท 3 = 30kVA estimated. If unbalanced, you'll have to separate the calculated load by line and go with the greatest line value.
    I'll never get there. No matter where I go, I'm always here.

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