Bonded Ground and Neutal in Outbuilding Panel

Discussion in 'Electrical and Wiring' started by VikingsFan, Apr 10, 2014.

  1. Apr 10, 2014 #1

    VikingsFan

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    I have a bit of a unique situation. My outbuilding has two hots and a Neutral coming into it's panel, but a dedicated / separate grounding rod. In this situation, should I bond the Neutral and Ground bus bars in the outbuilding sub panel? See the attached image for a better understanding.

    [​IMG]
     
  2. Apr 10, 2014 #2

    JoeD

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    Yes you should. That setup was permitted in the past. New installations require a separate ground in the feeder.
     
  3. Apr 10, 2014 #3

    Wuzzat?

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    Meaning there was no jumper?

    Meaning a cable with four conductors from main to outbuilding?


    It's not my place to come up with a rationale for the electrical code, but:

    Option 1, with outbuilding N & G unconnected, a person who is grounded at the outbuilding (let's say standing barefoot on wet ground) would see zero volts on outbuilding metal enclosures.

    Option 2, with outbuilding N & G connected, a person who is grounded at the outbuilding would see 2-3 v on outbuilding metal enclosures assuming current was being drawn by the outbuilding.

    Option 3, with outbuilding N & G connected through a four wire cable from the main building and with outbuilding N & G unconnected, a person who is grounded at the outbuilding would see the voltage difference between the ground at the outbuilding and the ground at the main building.
    This voltage is probably indeterminate and small unless the current density in the ground happens to be very high, like in a metropolitan area.

    I'd say go with option 1 but the electrical code people must have some good reason for picking option 3.

    These various option voltages can be tested with a multimeter and a heavy 120v load turned on in the outbuilding.
     
    Last edited: Apr 10, 2014
  4. Apr 11, 2014 #4

    VikingsFan

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    Thanks for the replies! I haven't encountered this situation before and wanted a second set of eyes. I also am of the opinion that they bus bars should be separated, but that's just because it's been drilled into me that you always keep them separate in sub. panels. If anyone else has other experience, or opinions, I would be glad to hear them!
     
  5. Apr 11, 2014 #5

    Wuzzat?

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  6. Apr 11, 2014 #6

    VikingsFan

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    OK, so it seems like it's a Single Point Ground vs. Distributed Single Point Ground, but I'm not sure that's applicable. It implies that I have an option of either using the common ground from the Service Panel, or tying the Service Panel Ground to the Neutral at multiple points with multiple earthing locations. I have neither choice. My choice is to either not tie the Neutral to a ground at all, or tie it into a separate ground altogether. The challenge is that there is no continuous ground connection from the Service Panel to the outbuilding Sub-Panel, and running one would be a challenge. The last bit of confusion comes in that I would like to add a 30A GFCI / Arc Fault Detection breaker to the outbuilding, but I'm not certain that it would work considering the issues with the ground.
     
  7. Apr 11, 2014 #7

    JoeD

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    Under current code you do not have that option. Past codes allowed for a three feed to out buildings and a ground rod except under certain conditions. Current code requires a four wire feed to out buildings and a ground for all circumstances.
     
  8. Apr 11, 2014 #8

    Wuzzat?

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    And I don't know of any way you can find out ahead of time.

    You'd have to gamble the price of this device on the likelihood that you don't get nuisance tripping once per day/week/month/year, balanced with whatever marginal additional safety you'd get.
    GFCIs give you some safety but I can't get credible numbers on this and I have my doubts about AFCIs.

    BTW, GFCIs don't need a ground to work and maybe the same is true for AFCIs.

    Putting this in perspective, people dying from electricity each year is about 15x less than from driving a car. Your odds are much better than this because you look before you leap.
     
    Last edited: Apr 11, 2014
  9. Apr 11, 2014 #9

    nealtw

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    I don't understand what the problem is?
     
  10. Apr 12, 2014 #10

    speedy petey

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    OK, if this is an existing installation it is FINE. The neutral IS bonded to the panel enclosure. It is treated just like a main panel.

    You have to remember, the ground rod and associated wire have NOTHING to do with the incoming feeder wire(s). A ground rod "ground" serves a completely different purpose.

    Not sure why you would even want to, but you CANNOT use a GFI or AFCI feeder breaker in cases like this. You'll have to protect everything from the sub-panel location or local devices.
     
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  11. Apr 12, 2014 #11

    VikingsFan

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    Makes total sense. I am looking to hook up a control panel for some power equipment that can be run wet. I can easily add a DIN mount AFCI to that panel, however, which should suit my purposes fine.

    I'm still not clear on the whole ground / neutral bonded vs. not bonded, but the consensus seems to be that they should be connected in this scenario. I would love to simply add a ground to the run from the main building to the outbuilding, but that would be a challenge. There's no pull string and its a buried run of Sealtite that seems to make a few sharp turns.

    Anyway, I appreciate all the feedback. I'm just trying to be safe here, and I'm glad there's a place I can get some solid advice.

    Thanks for all the great replies!
     
  12. Apr 12, 2014 #12

    Wuzzat?

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    That makes two of us.

    I will add that

    if
    you have a neutral conductor that is sensed by a GFCI and
    has a ground rod at each end,

    then
    the soil will be pushing current through the neutral and
    this may fool the GFCI because
    the current going out the hot lead is almost certain to be not the same as that returning on the neutral lead.

    Having just waded through the instructions for my income tax, you may notice that the electrical code is similar. They are a bunch of IF-THEN-ELSE statements but are not quite so clearly stated.

    Also, there are logical fallacies in the elec. code, probably because the people who wrote it are likely not trained in symbolic logic. Some percentage of electricians get tripped up on these fallacies.

    If you haven't read
    http://www.goodreads.com/book/show/6919310-how-math-can-save-your-life
    on symbolic logic or done programming and you want to understand these opaque and arcane documents, I'll pray for you. :D
    The burden for understanding is on the reader and it might be an undue burden. I'm sure this is true for the US Tax Code, and there is at least one CPA who agrees with me.
     
    Last edited: Apr 12, 2014

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