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Thread: EGC for subpanel

  1. #1
    Join Date
    Sep 2017
    Location
    Rock Hill, SC, USA
    Posts
    2

    EGC for subpanel

    My daughter's house has a 2 circuit 120/240 service entrance panel that supplies an Air Conditioner and a single multi circuit subpanel. My guess is that the subpanel originally served as the service entrance equipment, but at some point the air conditioner was installed and the 2 circuit panel was added to supply the air conditioner and the second circuit used to feeder the original power distribution panel.The neutral at the service entrance is connected to a grounding electrode. A 100 amp breaker supplies the sub panel (located at the other end of the house, about 60 feet away) through a 3-wire (2 conductor with bare neutral) cable.
    It is my understanding that a EGC should be provided between the service entrance panel and the subpanel and the EGC should be connected to the grounding electrode at the service entrance panel and to the isolated ground bus at the subpanel. I have 3 questions: 1. Can a new separate EGC be run alongside, but externally to the exposed feeder circuit supplying the subpanel?
    2. There is a 100 amp main breaker in the subpanel. Is a main breaker permitted in the subpanel?
    3. What is the minimum size of the "new" EGC?

  2. #2
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    11,742
    Are you doing the work or merely asking for code references?

    DIY questions are not allowed.

    Members can answer code questions.
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #3
    Join Date
    Sep 2017
    Location
    Rock Hill, SC, USA
    Posts
    2

    EGC for Sub-panelo

    I am not doing the work myself, but wanted to know what is required/permitted. Thanks for the clarification.

  4. #4
    Join Date
    Nov 2003
    Location
    Roanoke, VA.
    Posts
    4,189
    Quote Originally Posted by nculbert View Post
    My daughter's house has a 2 circuit 120/240 service entrance panel that supplies an Air Conditioner and a single multi circuit subpanel. My guess is that the subpanel originally served as the service entrance equipment, but at some point the air conditioner was installed and the 2 circuit panel was added to supply the air conditioner and the second circuit used to feeder the original power distribution panel.The neutral at the service entrance is connected to a grounding electrode. A 100 amp breaker supplies the sub panel (located at the other end of the house, about 60 feet away) through a 3-wire (2 conductor with bare neutral) cable.
    It is my understanding that a EGC should be provided between the service entrance panel and the subpanel and the EGC should be connected to the grounding electrode at the service entrance panel and to the isolated ground bus at the subpanel. I have 3 questions: 1. Can a new separate EGC be run alongside, but externally to the exposed feeder circuit supplying the subpanel?
    2. There is a 100 amp main breaker in the subpanel. Is a main breaker permitted in the subpanel?
    3. What is the minimum size of the "new" EGC?
    1. No. 300-5 (I)
    2. yes, not required but is permissible.
    3. #8 Copper or #6 aluminum. table 250.122
    Sometimes I don't know whether I'm the boxer or the bag.

  5. #5
    Join Date
    Jan 2009
    Location
    Maryland
    Posts
    11,742
    Quote Originally Posted by qcroanoke View Post
    1. No. 300-5 (I)
    I would say 300.3(B) may be a little more on target as both panels seem to be in a single building, but they say the same thing so it covers both bases.
    "Electricity is really just organized lightning." George Carlin


    Derek

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