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  1. #1

    Question Grounding method of detached building branch panel

    Sorry,
    My brain when dead on this one.

    Situation: Original living quarters (900 sq.ft.) with garage, built in 1995, and had its own main 200 amp. panel supplied by an underground service.
    A separate detached house was built in 1999 on the same piece of property within 20' of the original living quarters. The newer home has a 400 amp. main panel. The original main 200 amp. panel is now converted to a branch panel in the original detached structure and is being fed by a 60 amp. 240v. circuit through plastic electrical conduit run underground between the two panels. There is no ground run from the main 400 amp. panel to the 60 amp. branch panel through this conduit (only the two hots and a neutral). The branch panel is relying solely on its original grounding connections to its water piping and to its Ufer ground.
    Is a grounding conductor required from the main panel to the branch panel since this is a detached structure (and yes, the neutrals were still tied to the grounding buss in the branch panel - thank you sparky).

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  2. #2
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    Default Re: Grounding method of detached building branch panel

    Quote Originally Posted by Steve Kincaid View Post
    There is no ground run from the main 400 amp. panel to the 60 amp. branch panel through this conduit (only the two hots and a neutral).
    Actually, there *IS* a ground, it is just that the neutral is being used as a ground - which is not allowed for that installation.

    Yes, a "separate" grounding conductor is required between those two panels.

    Is a grounding conductor required from the main panel to the branch panel since this is a detached structure (and yes, the neutrals were still tied to the grounding buss in the branch panel - thank you sparky).
    Actually, more than that is required.

    From your description, the original service equipment (at the original house) is no longer being used as service equipment, yet the service is still running to that panel.

    The electrical system 'could have been all changed around' to reflect the new wiring and new location of the service equipment, but if the service equipment is anyplace but at the original structure and its panel ... what you are describing (at least what I am visualizing what you are describing) is all wrong.

    Here are some questions:
    - Where is the service now located?
    - Where is the service equipment panel?
    - The service equipment conductor (laterals from underground) go to which panel?
    - From that panel (in the above question) the *feeders* (no longer "service equipment conductors") go to where?
    - From the above question, the "feeders" *REQUIRE* 4 wires: 'hot' 'hot' 'neutral' 'ground', and less and you have a problem. 'Ground' "could be" metal conduit, however, you stated PVC, thus the "ground" must be a separate conductor - i.e., 4 conductors from the service equipment panel to any other panel.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  3. #3
    Jon Randolph's Avatar
    Jon Randolph Guest

    Default Re: Grounding method of detached building branch panel

    Quote Originally Posted by Jerry Peck View Post

    - From the above question, the "feeders" *REQUIRE* 4 wires: 'hot' 'hot' 'neutral' 'ground', and less and you have a problem. 'Ground' "could be" metal conduit, however, you stated PVC, thus the "ground" must be a separate conductor - i.e., 4 conductors from the service equipment panel to any other panel.
    Correct me if I am wrong, but I'm certain that the NEC will allow the other panel (sub, auxilliary, secondary, whatever you want to call it) to be grounded via a grounding rod, UFER ground or water piping if it meets the separation requirements from the main service panel ground.

    I realize that there are other issues with this service that are unclear on this post at this time, but the main home should have already had a ground at the time of construction. Unless this is grounded via the water pipes and they are shared between the buildings, it should be grounded, IMO.


  4. #4
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    Default Re: Grounding method of detached building branch panel

    (bold is mine)
    Quote Originally Posted by Jon Randolph View Post
    Correct me if I am wrong, but I'm certain that the NEC will allow the other panel (sub, auxilliary, secondary, whatever you want to call it) to be grounded via a grounding rod, UFER ground or water piping if it meets the separation requirements from the main service panel ground.
    "Will allow" I am assuming means 'instead of' being grounded back to the main grounding electrode system.

    Only if there are no metallic paths which connect the two structures together. I believe that is what you are referring to (see bold below).

    2005 NEC (bold is mine)
    - 250.32 Building(s) or Structure(s) Supplied by Feeder(s) or Branch Circuits.
    - - (A) Grounding Electrode. Building(s) or structure(s) are supplied by a feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with 250.50. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
    - - - Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non–current-carrying parts of all equipment. For the purpose of this section, a multi-wire branch circuit shall be considered as a single branch circuit.
    - - (B) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either 250.32(B)(1) or (2).
    - - - (1) Equipment Grounding Conductor. An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
    - - - (2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of
    - - - - (1) That required by 220.22
    - - - - (2) That required by 250.122
    - - (C) Ungrounded Systems. The grounding electrode(s) shall be connected to the building or structure disconnecting means.
    - - (D) Disconnecting Means Located in Separate Building or Structure on the Same Premises. Where one or more disconnecting means supply one or more additional buildings or structures under single management, and where these disconnecting means are located remote from those buildings or structures in accordance with the provisions of 225.32, Exception Nos. 1 and 2, all of the following conditions shall be met:
    - - - (1) The connection of the grounded conductor to the grounding electrode at a separate building or structure shall not be made.
    - - - (2) An equipment grounding conductor for grounding any non–current-carrying equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conductors to a separate building or structure and bonded to existing grounding electrode(s) required in Part III of this article, or, where there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed where a separate building or structure is supplied by more than one branch circuit.
    - - - (3) Bonding the equipment grounding conductor to the grounding electrode at a separate building or structure shall be made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building or structure.
    - - (E) Grounding Electrode Conductor. The size of the grounding electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  5. #5
    Jon Randolph's Avatar
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    Default Re: Grounding method of detached building branch panel

    Quote Originally Posted by Jerry Peck View Post
    (bold is mine)


    "Will allow" I am assuming means 'instead of' being grounded back to the main grounding electrode system.

    Only if there are no metallic paths which connect the two structures together.
    Quote Originally Posted by Jon Randolph View Post
    Unless this is grounded via the water pipes and they are shared between the buildings, it should be grounded, IMO.
    Yeah, that is what I meant. I specified water piping, but I should have said any matallic path.


  6. #6
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    Default Re: Grounding method of detached building branch panel

    Quote Originally Posted by Jon Randolph View Post
    Unless this is grounded via the water pipes and they are shared between the buildings, it should be grounded, IMO.
    Quote Originally Posted by Jon Randolph View Post
    Yeah, that is what I meant. I specified water piping, but I should have said any matallic path.
    Jon,

    Nope, not then either.

    The underground water pipe is not allowed to be used for that use. It may be 'used as' one of the grounding electrodes if it meets the requirements (at least 20 feet long underground), but is does not meet the requirements for 'grounding electrode conductors' or bonding jumpers between grounding electrodes.

    Thus, is there is a metal water pipe, you would still install all the present grounding electrodes at the second structure, and you would still be required to run a separate grounding conductor (4 wires) to that building.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  7. #7
    Mark Jones's Avatar
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    Default Re: Grounding method of detached building branch panel

    Hi Steve,

    I would think of the UFER in the original house as needed in case of lightning or some other unusual (?) situation. The grounding conductor that should be run between the two panels would be mainly to make the 60 amp breaker trip in case of a short in the wiring of the original house, or the feeders leading to it. (I assume that the 60 amp breaker is in the 400 amp panel.)

    Many of us (myself included,) could spend a lot more time studying the complicated and interesting subject of grounding and bonding.

    Safe Haven Mark


  8. #8
    Shannon Guinn's Avatar
    Shannon Guinn Guest

    Default Re: Grounding method of detached building branch panel

    Jerry, this may be off the thread but you are a wealth of information and if I'm ever down your way I would love to buy you a cup of coffee just for the small talk, but I have one question, do you still work or are you retired? Don't see how you could still work and have that many posts on the forum, either way don't stop.


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