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    Shared Neutrals

    What section in the code will give me direction on shared neutrals? I'm doing some work in an older building and they have as many as 11 20A/1P breakers on a single neutral conductor, on a 3PH panel. They are trying to aviod rewiring the entire building, but some of this work clearly needs to be redone.

    Is there a section I can reference when stating my case.

    #2
    For code cycles before 2011, article section 225.7 was the closest you will find, it specifically allowed it for outside lighting but, with this being the case and nothing else where prohibitting it it seemed it could be used for other applications as well.

    Roger
    Moderator

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      #3
      I stumbled upon 215.4, I think I found what I'm looking for.

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        #4
        Originally posted by rjken1969 View Post
        I stumbled upon 215.4, I think I found what I'm looking for.
        So is this a feeder or a branch circuit. Certainly you can feed a panel with one neutral however there are limits to branch circuits.

        For the 2011 look at 200.4 but these installs were done before then as Roger was mentioning.
        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

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          #5
          Originally posted by roger View Post
          For code cycles before 2011, article section 225.7 was the closest you will find, it specifically allowed it for outside lighting but, with this being the case and nothing else where prohibitting it it seemed it could be used for other applications as well.

          Roger
          I agree. Nothing specifically prohibited a common neutral for MWBC's prior to 2011 NEC.
          I will have achieved my life's goal if I die with a smile on my face.

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            #6
            Originally posted by rjken1969 View Post
            I stumbled upon 215.4, I think I found what I'm looking for.
            Keep in mind 215 is for feeders not branch circuits.
            I live for today, I'm just a day behind.

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              #7
              Originally posted by rjken1969 View Post
              What section in the code will give me direction on shared neutrals? I'm doing some work in an older building and they have as many as 11 20A/1P breakers on a single neutral conductor, on a 3PH panel.
              Can you explain how this didn't burn up over time? Was the single neutral oversized?
              Rob

              Moderator

              All responses based on the 2014 NEC unless otherwise noted

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                #8
                Originally posted by infinity View Post
                Can you explain how this didn't burn up over time? Was the single neutral oversized?
                Depending on the loads:

                Loads were lucky enough to be reasonably balanced and no significant overheating occurred?

                Circuits were lightly loaded, or maybe little demand most of the time.

                If there would have been 12 circuits instead of 11 and all were identical load, the neutral current should be zero. Assuming they are all in demand simultaneously - which could possibly happen if this is lighting circuits.
                I live for today, I'm just a day behind.

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                  #9
                  Originally posted by kwired View Post
                  Depending on the loads:

                  Loads were lucky enough to be reasonably balanced and no significant overheating occurred?

                  Circuits were lightly loaded, or maybe little demand most of the time.

                  If there would have been 12 circuits instead of 11 and all were identical load, the neutral current should be zero. Assuming they are all in demand simultaneously - which could possibly happen if this is lighting circuits.
                  Until somebody turns on exactly the right (wrong) combination of 6 of the 12 lighting circuits.

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                    #10
                    I guess that would depend on what type of lighting loads. Do you think that if they all were fluorescent lighting loads the neutral would have burnt up a long time due to triplen harmonics?
                    Rob

                    Moderator

                    All responses based on the 2014 NEC unless otherwise noted

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                      #11
                      Originally posted by GoldDigger View Post
                      Until somebody turns on exactly the right (wrong) combination of 6 of the 12 lighting circuits.
                      Maybe they were always all on at same time.

                      Originally posted by infinity View Post
                      I guess that would depend on what type of lighting loads. Do you think that if they all were fluorescent lighting loads the neutral would have burnt up a long time due to triplen harmonics?
                      Would that be a problem with magnetic ballasts? Remember those? I can see that with electronic ballasts. We were not told how old this installation is or what the loads actually are.
                      I live for today, I'm just a day behind.

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                        #12
                        Originally posted by kwired View Post
                        Maybe they were always all on at same time.



                        Would that be a problem with magnetic ballasts? Remember those? I can see that with electronic ballasts. We were not told how old this installation is or what the loads actually are.
                        I know, the OP was lacking in information that's why I asked him to provide some detail.
                        Rob

                        Moderator

                        All responses based on the 2014 NEC unless otherwise noted

                        Comment


                          #13
                          Originally posted by rjken1969 View Post
                          ...I'm doing some work in an older building and they have as many as 11 20A/1P breakers on a single neutral conductor, on a 3PH panel...
                          How did they get 12 #12s into a single 76 - or did they use a bug? I can't imagine what the wiring in that place must look like.
                          Peter A.

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                            #14
                            I have no idea what type of circuits these are, it's a rat's nest of an installation. It's probably the worst I've seen. Forty years and tens of contractors, most of which were not licensed.

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                              #15
                              Originally posted by rjken1969 View Post
                              I have no idea what type of circuits these are, it's a rat's nest of an installation. It's probably the worst I've seen. Forty years and tens of contractors, most of which were not licensed.
                              You can't tell if they are branch circuits or feeders?

                              If they are feeders they will be supplying other overcurrent devices such as a panelboard or taps to fused disconnects or something similar that ends up being overcurrent device(s).

                              If they are branch circuits they will be supplying outlets - lighting, receptacles, other utilization equipment.
                              I live for today, I'm just a day behind.

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