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Thread: Bonding in transformer and panel?

  1. #1
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    Bonding in transformer and panel?

    I have a question about if you bond in the transformer, then why would you also bond in the panel? I was always told and understood that you bond once at the transformer where the service starts and nowhere else. If you bond at transformer and panel then you are paralleling the neutral and ground. It's like running two neutrals down to panel from transformer. Any thoughts? Thanks

  2. #2
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    Since the POCO service transformer secondary neutral is bonded to POCO ground, you might think that you should not have another bond at your service disconnect.
    But POCO does not carry a grounding wire to your panel, just the grounded neutral. If you do not bond your building EGCs to the POCO neutral there will not be an effective fault clearing path back to the transformer if there is a hot to ground fault on the premises.
    The earth electrodes do not form a low enough impedance connection to clear a fault.

  3. #3
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    Quote Originally Posted by Ibew journeyman View Post
    I have a question about if you bond in the transformer, then why would you also bond in the panel? I was always told and understood that you bond once at the transformer where the service starts and nowhere else. If you bond at transformer and panel then you are paralleling the neutral and ground. It's like running two neutrals down to panel from transformer. Any thoughts? Thanks
    This is a service and not just an SDS correct?

    Welcome to the Forum.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    Quote Originally Posted by infinity View Post
    This is a service and not just an SDS correct?

    Welcome to the Forum.
    Yes some clarification is needed on that.

    If he is talking about services - unless your service is medium voltage level the transformer is not subject to NEC it is controlled by the POCO. POCO's typically use a MGN type of system -there is a grounding electrode at nearly every structure they have on the system and it connects to the MGN at all of them.

  5. #5
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    Sorry guys, hears a little more info.. transformer is in a building being fed off of MDP. 480 primary/ 208 secondary to feed panel. I bonded in the transformer and was told that I needed to bond also in the panel. I have never bonded twice in two separate locations. My argument is that the panel would be considered like a sub panel and that you don't bond in there because I already established a bond at the transformer and bonding in the panel as well would parallel the neutral and ground wire. It would be like running two neutrals down to the panel with no effective ground. Am I correct?
    Thanks

  6. #6
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    Quote Originally Posted by Ibew journeyman View Post
    Sorry guys, hears a little more info.. transformer is in a building being fed off of MDP. 480 primary/ 208 secondary to feed panel. I bonded in the transformer and was told that I needed to bond also in the panel. I have never bonded twice in two separate locations. My argument is that the panel would be considered like a sub panel and that you don't bond in there because I already established a bond at the transformer and bonding in the panel as well would parallel the neutral and ground wire. It would be like running two neutrals down to the panel with no effective ground. Am I correct?
    Thanks
    You are correct. You bond in only one location, can be either one, your choice.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  7. #7
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    Quote Originally Posted by infinity View Post
    You are correct. You bond in only one location, can be either one, your choice.
    Most of the time yes, but we should note there is an exception that allows bonding in both locations.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #8
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    Quote Originally Posted by electrofelon View Post
    Most of the time yes, but we should note there is an exception that allows bonding in both locations.
    What exception is that?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  9. #9
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    250.30(A)(1) Exception No. 2

    Roger
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  10. #10
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    Quote Originally Posted by roger View Post
    250.30(A)(1) Exception No. 2

    Roger
    Ah thanks, I forgot about that one.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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