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Thread: Ground rod on a subpanel in an attached building

  1. #1
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    Ground rod on a subpanel in an attached building

    While in understand that a ground rod is required on a detached building's subpanel, is there anything that says you cannot put a ground rod on a subpanel that is in the same structure as the main panel? I have a 100 amp sub panel 220V with a separate neutral and ground coming from the main panel. I've always added a ground rod to a subpanel when it was reasonable to install one. My understanding has always been that while not required, it is against code to do it. I'm being told that you can't have a ground rod connected to a subpanel even if you still have an equipment grounding conductor. No code was given to support it but I can't find anything stating either way on this. Does anyone know any code sections stating either way?

    Thanks
    TW

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    Quote Originally Posted by TWControls View Post
    While in understand that a ground rod is required on a detached building's subpanel, is there anything that says you cannot put a ground rod on a subpanel that is in the same structure as the main panel? I have a 100 amp sub panel 220V with a separate neutral and ground coming from the main panel. I've always added a ground rod to a subpanel when it was reasonable to install one. My understanding has always been that while not required, it is against code to do it. I'm being told that you can't have a ground rod connected to a subpanel even if you still have an equipment grounding conductor. No code was given to support it but I can't find anything stating either way on this. Does anyone know any code sections stating either way?

    Thanks
    TW
    Per 250.54 it would be allowed but it would have to isolated from the neutral and basically a waste of materials and labor.

    Roger
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  3. #3
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    Quote Originally Posted by TWControls View Post
    While in understand that a ground rod is required on a detached building's subpanel, is there anything that says you cannot put a ground rod on a subpanel that is in the same structure as the main panel? I have a 100 amp sub panel 220V with a separate neutral and ground coming from the main panel. I've always added a ground rod to a subpanel when it was reasonable to install one. My understanding has always been that while not required, it is against code to do it. I'm being told that you can't have a ground rod connected to a subpanel even if you still have an equipment grounding conductor. No code was given to support it but I can't find anything stating either way on this. Does anyone know any code sections stating either way?

    Thanks
    TW
    Nope, it's permitted and called by the NEC an auxiliary grounding electrode. Roger gave you the code reference 250.54.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    Thanks Roger and Rob. That is what I was looking for.

  5. #5
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    It can also be part of the conventional GES and located at/near a subpanel, but it must then be connected back to the rest of the GES by a conductor that is sized as a ground bonding jumper rather than sized as an EGC.
    The open question for me is whether you can share that bonding jumper with the EGC in the same way that you can share the GEC and EGC functions.

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    Quote Originally Posted by GoldDigger View Post
    It can also be part of the conventional GES and located at/near a subpanel, but it must then be connected back to the rest of the GES by a conductor that is sized as a ground bonding jumper rather than sized as an EGC.
    The open question for me is whether you can share that bonding jumper with the EGC in the same way that you can share the GEC and EGC functions.
    You can, but you must meet all the requirements for both a GEC and an EGC [unspecified 2008 and prior; prohibited 2011 NEC 250.121; permitted 2014 NEC 250.12 Exception], which in part includes running it with the feeder conductors.
    Last edited by Smart $; 09-02-17 at 02:29 AM.
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  7. #7
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    Quote Originally Posted by Smart $ View Post
    You can...
    I should add that I see no purpose taking it beyond an auxiliary electrode connected via EGC for just a single ground rod.
    I will have achieved my life's goal if I die with a smile on my face.

  8. #8
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    Quote Originally Posted by Smart $ View Post
    I should add that I see no purpose taking it beyond an auxiliary electrode connected via EGC for just a single ground rod.
    I agree and 250.54 clearly states that it does not need to be included as part of the building GES.

    250.54 Auxiliary Grounding Electrodes. One or moregrounding electrodes shall be permitted to be connected to
    the equipment grounding conductors specified in 250.118
    and shall not be required to comply with the electrode
    bonding requirements of 250.50 or 250.53(C) or the resis-
    tance requirements of 250.53(A)(2) Exception, but the
    earth shall not be used as an effective ground-fault current
    path as specified in 250.4(A)(5) and 250.4(B)(4).
    250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are
    present at each building or structure served shall be bonded
    together to form the grounding electrode system
    . Where
    none of these grounding electrodes exist, one or more of
    the grounding electrodes specified in 250.52(A)(4) through
    (A)(8) shall be installed and used.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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