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    Grounding Ring Sizing

    Hello,

    I have a building of 8 appartments with 100A Panelboard for each appartment. Each panel is fed by 50 mm2 cable from a main distribution board which is around 50 meter away from the building. So 8 cables are coming into the building.

    What is the enough size for a grounding ring cable that will go around the building? Following 250.66 will 25 mm2 of cable ring around the building be enough?

    Is following 250.52(A)(4) minimum conductor size of 2 AWF is a must in this case?

    Same question for another building with 59 appartments + 59 panels + 59 Feeders of 50 mm2 for each appartment? what would be the minimum size here?

    Many thanks

    #2
    I did not think the ground ing needed to be any larger than a #2AWG. 250.66(C) and 250.52(A)(4)
    They say I shot a man named Gray and took his wife to Italy
    She inherited a million bucks and when she died it came to me
    I can't help it if I'm lucky

    Comment


      #3
      Originally posted by Dennis Alwon View Post
      I did not think the ground ing needed to be any larger than a #2AWG. 250.66(C) and 250.52(A)(4)
      My question is that can I go lower than # 2? and on what basis I can reduce the size of the cable? Shall I consider in this case largest feeder (here all are equal) or I will use sum of feeders?

      Thank you

      Comment


        #4
        Well I read it as you cannot use smaller than #2 no matter what size service as well as it does not need to be larger than the ground ring size (#2 or larger based on 250.66). It appears the gec to the ring can be sized to 250.66 so it can be smaller. GEC is based on service size not feeder unless it is a detached structure.
        Last edited by Dennis Alwon; 02-20-11, 01:16 PM.
        They say I shot a man named Gray and took his wife to Italy
        She inherited a million bucks and when she died it came to me
        I can't help it if I'm lucky

        Comment


          #5
          Let me state it in another way and sorry for repitition but still I see it not logical ( I am new to NEC):

          CASE 1:

          1 BUILDING with 59 Appartments (6 Stories)
          Each appartment Fed with a feeder from the Main Site Distribution Board with a 4x #0.
          Main Breaker for each appartment 100Amps

          CASE 2:

          1 Building with 8 Appartments
          Each appartment Fed with a feeder from the Main Site Distribution Board with a 4x #0.
          Main Breaker for each appartment 100Amps

          How can I design the Grounding Ring? What is the size of the cable?

          Referring to table 250.66 I can use # 6 Cable. Am I referring to correct table? Is this size for the ground ring itself or only the cable to connect the panel to the ring?

          Is there a minimum size for the grounding rod to be burried on the 4 corners of the building? I am using 4'. is this complying with NEC?

          Thank you

          Comment


            #6
            Okay the ground ring needs to be size from T250.66 based on the sum of the parallel feeds of the service entrance conductors. From there just pull the same size gec to the ring from the main distribution box. It will never be larger than 3/0.

            No need to size each apartment to the ground ring.
            They say I shot a man named Gray and took his wife to Italy
            She inherited a million bucks and when she died it came to me
            I can't help it if I'm lucky

            Comment


              #7
              For the money, a ufer ground will be as effective and less cost, if you have a choice.
              Moderator-Washington State
              Ancora Imparo

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