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Interpretation of 310.15(B)(6)

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    Interpretation of 310.15(B)(6)

    This section states that conductors as listed in the table shall be allowed for service conductors that act as the main power feeder. But then they define the main power feeder to be on the load side of the disconnect. Has anybody had an issue with this? What happened?

    #2
    I don't understand why you think there might be an issue. You can use that article and its associated table for the service conductors (i.e., upstream of the main disconnect) or for the main feeder (i.e., downstream of the main disconnect).

    By the way, it would help if you let us know what NEC edition you are using. I use the 2014, and that article has been renumbered. You must be on 2008 or earlier.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

    Comment


      #3
      Originally posted by dema View Post
      This section states that conductors as listed in the table shall be allowed for service conductors that act as the main power feeder. But then they define the main power feeder to be on the load side of the disconnect. Has anybody had an issue with this? What happened?
      "Acting as" is not the same as "is". A feeder cannot exist on the line side of a service disconnect.

      Comment


        #4
        Originally posted by dema View Post
        This section states that conductors as listed in the table shall be allowed for service conductors that act as the main power feeder. But then they define the main power feeder to be on the load side of the disconnect. Has anybody had an issue with this? What happened?
        Not sure what you are asking but this covers both service wires and feeder wires such as a subpanel. The sub would have to supply the entire dwelling to be able to use the table though.
        In short, to use the table, the wires (service or feeder) have to serve the entire load.
        [COLOR=navy]If you aim at nothing, you will hit it every time![/COLOR]

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          #5
          Actually George, he misquoted the article.
          Originally posted by dema View Post
          This section states that conductors as listed in the table shall be allowed for service conductors that act as the main power feeder.
          No it doesn't. It states that conductors, as shown in the table, are "permitted as . . . service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder. . . ." This quote is from the 2008 NEC.

          Charles E. Beck, P.E., Seattle
          Comments based on 2017 NEC unless otherwise noted.

          Comment


            #6
            The only "issue" that I have encountered is one where the E/C does not understand "main power feeder" and attempts to use this Table for situations where the feeder does not supply "all loads associated with the dwelling unit".
            At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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              #7
              Originally posted by augie47 View Post
              The only "issue" that I have encountered is one where the E/C does not understand "main power feeder" and attempts to use this Table for situations where the feeder does not supply "all loads associated with the dwelling unit".
              That and it is easy to assume that it applies to all dwellings - when it in fact says "120/240 volt", so a typical multi-family application supplied by 208/120 can't use it either.
              I live for today, I'm just a day behind.

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                #8
                Thank you

                The trouble arose because main power feeder is defined within the verbiage as being between the disconnect and the panel. Therefore, if there is no disconnect, does it still apply?

                I think this code section is worded badly because of that. It states that it applies only for the main power feeder, refers to the service feeders as being among other things that constitute a main power feeder, and then says "For application of this section the main power feeder shall be between the main power disconnect and the panel it supplies" So they took back what they just said. Very clearly in fact.

                My understanding is that in practice you have used that same wire size for the service feeder and had it approved and never thought about it again. That says a lot. Thank you very much.

                Comment


                  #9
                  Originally posted by dema View Post
                  The trouble arose because main power feeder is defined within the verbiage as being between the disconnect and the panel. Therefore, if there is no disconnect, does it still apply?

                  I think this code section is worded badly because of that. It states that it applies only for the main power feeder, refers to the service feeders as being among other things that constitute a main power feeder, and then says "For application of this section the main power feeder shall be between the main power disconnect and the panel it supplies" So they took back what they just said. Very clearly in fact.

                  My understanding is that in practice you have used that same wire size for the service feeder and had it approved and never thought about it again. That says a lot. Thank you very much.
                  When ever NEC says "for application of this section" you can disregard any general purpose or even art 100 definitions and go with whatever information that follows, but that statement is limited to the section it is a part of or refers to.

                  It does complicate things a little when they mention "power feeder" when "feeder" is a NEC defined term though.
                  I live for today, I'm just a day behind.

                  Comment


                    #10
                    Originally posted by dema View Post
                    The trouble arose because main power feeder is defined within the verbiage as being between the disconnect and the panel. Therefore, if there is no disconnect, does it still apply?
                    Yes, because the disconnect would be the Main Breaker at the Service Point and the table would apply to the Service Entrance or Service-Lateral Conductors. If there is only one feeder leaving this panel and feeds a downstream panel that serves all the loads it could also use the table to size this feeder.

                    Roger
                    Moderator

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                      #11
                      I'm not seeing the confusion. Service conductors exist on the line side of the service disconnect, and feeders exist on the load side. There is no such thing as a "feeder" that has no disconnect on its line side.

                      Comment


                        #12
                        Look at the definition of feeder in article 100. Now if that feeder feeds the entire load of the dwelling then it may use the table otherwise it must use the standard tables

                        Feeder. All circuit conductors between the service equipment,
                        the source of a separately derived system, or other
                        power supply source and the final branch-circuit overcurrent
                        device.
                        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


                          #13
                          The confusion is in the fact that they say that it applies to the service entrance conductors that serve as a main power feeder and then they say that for application of this section the main power feeder is between the disconnect and the panel - well, that is contradicting what they just said. The service conductor is NOT between the main disconnect and and the panel, it is on the line side. So first they say that the line side counts, and then they say that the table only applies to the main power feeder which is only on the load side.

                          If you read what they say literally, it makes your head spin off like those little toys that launch a little helicopter blade into the air.

                          Read what I mean not what I say?

                          Comment


                            #14
                            Originally posted by dema View Post
                            The confusion is in the fact that they say that it applies to the service entrance conductors that serve as a main power feeder and then they say that for application of this section the main power feeder is between the disconnect and the panel - well, that is contradicting what they just said. The service conductor is NOT between the main disconnect and and the panel, it is on the line side. So first they say that the line side counts, and then they say that the table only applies to the main power feeder which is only on the load side.

                            If you read what they say literally, it makes your head spin off like those little toys that launch a little helicopter blade into the air.

                            Read what I mean not what I say?
                            This is how the first part is broken down properly:

                            ...shall be permitted as 120/240-volt, 3-wire, single-phase...
                            [LIST][*]service-entrance conductors,[*]service-lateral conductors, and[*]feeder conductors that serve as the main power feeder[/LIST]
                            ...to each dwelling unit...
                            The main power feeder portion only applies to feeder conductors.
                            [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

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                              #15
                              Service conductor are not feeders. That is why I posted the definition of feeder. The service conductors are the conductors that go from the service to the first disconnecting means. From there there are branch circuits and feeders.

                              Think of it this way. If you have a meter with service conductors that go to a main lug panel (using the 6 handle rule) then those conductors can take advantage of the residential table. Now if you have one dp breaker in that panel and it feeds another panel that has all the loads in the dwelling then you can use the table for those feeder conductors also. However, if I add another breaker in the main panel , say for an a/c, then the feeder going to the sub panel cannot take advantage of the residential panel. Same is true if the service panel had a main.

                              We often have a feed thru main breaker panel 200 amp but we cannot take advantage of the resi table if we install any other breakers in the panel
                              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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