Announcement

Collapse
No announcement yet.

2011 NEC, 250.118 (10) undersized ground conductor ???

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    2011 NEC, 250.118 (10) undersized ground conductor ???

    This section talks about using the metallic sheath in combination with the ground conductor. Is this section allowing the ground conductor to be undersized and not meet table 250.122 requirements ???

    #2
    If you read it again it says "The combined metallic sheath and uninsulated equipment grounding/bonding conductor". Sounds like the reference is actually for a cable like MC-ap where the sheath and the bare bonding conductor act in concert to form the EGC.
    Rob

    Moderator

    All responses based on the 2017 NEC unless otherwise noted

    Comment


      #3
      We have a MC type cable, and the ground conductor is smaller than Table 250.122. At this point, I do not know if it is listed as stated in 250.118 (10) c. But, if it is listed, does this mean that the ground conductor can be smaller than what it should be per T250.122 ?

      Comment


        #4
        Originally posted by Ranger86 View Post
        We have a MC type cable, and the ground conductor is smaller than Table 250.122. At this point, I do not know if it is listed as stated in 250.118 (10) c. But, if it is listed, does this mean that the ground conductor can be smaller than what it should be per T250.122 ?
        Exactly what do you have?
        Size and number of conductors.
        Exact labeling (on packaging or reel; may be on binder wrap between armor and conductors).

        Insulated EGC's in MC cable are sized for typical OCPD ratings. Other EGC sizes are available by special order.

        There are several "flavors" of Type MC cable, and we don't know what you have until you tell us.

        We don't read minds... at least not very well at times.
        I will have achieved my life's goal if I die with a smile on my face.

        Comment


          #5
          Originally posted by Ranger86 View Post
          We have a MC type cable, and the ground conductor is smaller than Table 250.122. At this point, I do not know if it is listed as stated in 250.118 (10) c. But, if it is listed, does this mean that the ground conductor can be smaller than what it should be per T250.122 ?

          If this ground conductor is actually an EGC then in cable sizes #14, #12 and #10 AWG the EGC must be the same size. Once you exceed #10 AWG then the EGC will be smaller as permitted in T250.122.
          Rob

          Moderator

          All responses based on the 2017 NEC unless otherwise noted

          Comment


            #6
            Originally posted by infinity View Post
            If you read it again it says "The combined metallic sheath and uninsulated equipment grounding/bonding conductor". Sounds like the reference is actually for a cable like MC-ap where the sheath and the bare bonding conductor act in concert to form the EGC.
            Thats exactly what that provision is for....Things like MC-SG and MC-AP type products.
            *All code responses are based on the 2017 National Electrical Code®[NEC®]

            Comment


              #7
              Originally posted by MasterTheNEC View Post
              Thats exactly what that provision is for....Things like MC-SG and MC-AP type products.
              OK. Thank you. I wish that somewhere in 250.118 (10), it had "ground conductor can be smaller than the minimum required per T250.122". This would make it much easier to read. Thanks again !!!!
              I will check on the MC cable UL listings.

              Comment


                #8
                Originally posted by Smart $ View Post
                Exactly what do you have?
                Size and number of conductors.
                Exact labeling (on packaging or reel; may be on binder wrap between armor and conductors).

                Insulated EGC's in MC cable are sized for typical OCPD ratings. Other EGC sizes are available by special order.

                There are several "flavors" of Type MC cable, and we don't know what you have until you tell us.

                We don't read minds... at least not very well at times.
                I have a couple of scenarios, here is one of them ....
                A parallel 400A feeder, 400A OCPD, the conductor size also had to be increased for voltage drop. So, I ended up with parallel 4/0 phase & neutral with #2 ground. The 4/0 MC cable comes with #4 ground conductor.

                Comment


                  #9
                  Originally posted by Ranger86 View Post
                  I have a couple of scenarios, here is one of them ....
                  A parallel 400A feeder, 400A OCPD, the conductor size also had to be increased for voltage drop. So, I ended up with parallel 4/0 phase & neutral with #2 ground. The 4/0 MC cable comes with #4 ground conductor.
                  You cannot use standard MC for that application. You will have to special order MC with the appropriate EGC size (note a few manufacturers offer non-standard-size EGC in there product listing, but your local supply house usually does not stock them).
                  I will have achieved my life's goal if I die with a smile on my face.

                  Comment


                    #10
                    Originally posted by Smart $ View Post
                    You cannot use standard MC for that application. You will have to special order MC with the appropriate EGC size (note a few manufacturers offer non-standard-size EGC in there product listing, but your local supply house usually does not stock them).
                    This is the part that gets confusing to me..... So, 250.118 (10), does it or does it not allow the ground conductor to be smaller than what the T250.122 requires ?

                    Comment


                      #11
                      Originally posted by Ranger86 View Post
                      This is the part that gets confusing to me..... So, 250.118 (10), does it or does it not allow the ground conductor to be smaller than what the T250.122 requires ?
                      It does not. The general statement to (10) says effective ground-fault current path... and that effectiveness is determined by an EGC sized per 250.122. Where the combined sheath and conductor is listed as an EGC, the listing would have to indicate an effective size in order for 250.122 to be applied correctly. AFAIK, such are usually redundant EGC's, and compliance is met by the 'primary' EGC.
                      I will have achieved my life's goal if I die with a smile on my face.

                      Comment


                        #12
                        Originally posted by Smart $ View Post
                        It does not. The general statement to (10) says effective ground-fault current path... and that effectiveness is determined by an EGC sized per 250.122. Where the combined sheath and conductor is listed as an EGC, the listing would have to indicate an effective size in order for 250.122 to be applied correctly. AFAIK, such are usually redundant EGC's, and compliance is met by the 'primary' EGC.
                        Thank you everybody, for the clarification on this.

                        Comment


                          #13
                          Ranger-- when we talk about T. 250.122 you should say equipment grounding conductor not ground conductor. A neutral can be looked at as a ground conductor because it is grounded. One normally says grounded conductor or neutral for the neutral-- although there is a technical difference and the grounding conductor is the equipment grounding conductor

                          This helps us understand what you are asking. At first I thought you wanted to know if the grounded conductor could be smaller than the equipment grounding conductor. Thanks
                          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


                            #14
                            Originally posted by Dennis Alwon View Post
                            Ranger-- when we talk about T. 250.122 you should say equipment grounding conductor not ground conductor. A neutral can be looked at as a ground conductor because it is grounded. One normally says grounded conductor or neutral for the neutral-- although there is a technical difference and the grounding conductor is the equipment grounding conductor

                            This helps us understand what you are asking. At first I thought you wanted to know if the grounded conductor could be smaller than the equipment grounding conductor. Thanks
                            Sorry about that, thanks for letting me know. I am trying to get the manufacturer data to verify the listings of the MC cable... the manufacturer was bought by another one around 10 years ago so I am hoping they have that data.

                            Comment


                              #15
                              Originally posted by Ranger86 View Post
                              Sorry about that, thanks for letting me know. I am trying to get the manufacturer data to verify the listings of the MC cable... the manufacturer was bought by another one around 10 years ago so I am hoping they have that data.
                              Just curious, exactly what data are you looking for?
                              Rob

                              Moderator

                              All responses based on the 2017 NEC unless otherwise noted

                              Comment

                              Working...
                              X