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    #46
    Originally posted by jap View Post
    If the 200 amp panel is drawing say 150 amps, and,you subfed the 100 amp panel from the 200 amp panel, and, the 100 amp panel is drawing 50 amps (200 amps total), and, the service conductors are rated at 200 amps, you will most likely trip the 200 amp breaker even though you haven't overloaded the 200 amp rated service conductors if run this way for any length of time.

    In that same scenario, with a service tap, you would not trip the 200 amp, and, you still would not have overloaded the 200 amp rated service conductors.

    JAP>
    If run that way for any length of time then you likely don't have 125% of continuous load and 100% of non continuous load calculated correctly if your end result was a 200 amp conductor. Not landing on a "standard" overcurrent device however doesn't require 125% of continuous load - in that case a 200 amp conductor is good for 200 amps continuous. 4/0 aluminum is too small unless 310.15(B)(7) can be applied, 250 aluminum has 5 amps to spare and 3/0 copper is right on.

    Originally posted by charlie b View Post


    I can't quite get here from there. That article points you to four other articles that essentially address means and methods. But they do not have rules similar to the feeder tap rules that include requirements for conductor sizes (as compared to the conductor being tapped), distance limits, and overcurrent protection at the end of the tap. Even if I knew the AWG size of the service conductors and the distance between their new pull box and the new panel, how could I judge whether the installation would meet all relevant NEC requirements, especially as I don't know where any such requirements would be found?

    I am still looking at this as a "non-trivial exercise."
    EF kind of addressed it - service conductors are different from feeders and branch circuit conductors in that there is no overcurrent protection ahead of the conductor. Feeder tap rules are meaningless to apply or compare to similar situations involving service conductors because of this.

    Originally posted by electrofelon View Post
    I think you are over thinking this. There arent really specific "tap rules" for SEC, at least they arent called that, but see 230.40, 230.70,230.71, 230.72, 230.90(A) EX 3. I think what you are hung up on is "tapping" a SEC with smaller sized wire - its fine, there is no OCPD there anyway so it doesnt matter that it is smaller. Best you can do is give it overload protection as required in 230.90. Think about it, we "split" SEC into multiple/smaller sets all the time: A bussed gutter above a bunch of meters, a multi gang meter socket without disconnects, etc......
    I live for today, I'm just a day behind.

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      #47
      Originally posted by infinity View Post
      The only potential issue I see is the possible overloading of the existing conductors. If a load calculation proves that they're sufficient then there is no issue. Also there should not be a "#6 ground" in the raceway with the new SEC's.
      I agree.

      Essentially, this is no different then service conductors entering a gutter and splitting to multiple service disconnects. In this case they are just adding the pull box after the fact.

      As long as the conductors meet the calculated load, it's time to move forward.

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        #48
        Originally posted by kwired View Post
        If run that way for any length of time then you likely don't have 125% of continuous load and 100% of non continuous load calculated correctly if your end result was a 200 amp conductor. Not landing on a "standard" overcurrent device however doesn't require 125% of continuous load - in that case a 200 amp conductor is good for 200 amps continuous. 4/0 aluminum is too small unless 310.15(B)(7) can be applied, 250 aluminum has 5 amps to spare and 3/0 copper is right
        310.15(B)(7) informational note #2
        4/0 Aluminum and 2/0 CU is good for 200A on services



        Sent from my iPhone using Tapatalk

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          #49
          Originally posted by Malywr View Post
          310.15(B)(7) informational note #2
          4/0 Aluminum and 2/0 CU is good for 200A on services



          Sent from my iPhone using Tapatalk
          You are reviving something that hasn't had a post for about 4 months so I may be missing something, but I did say "unless 310.15(B)(7) applies". Without the allowances of (B)(7) 4/0 aluminum only has an ampacity of 180 and 2/0 copper only has an ampacity of 175.

          What (B)(7) does isn't exactly an ampacity adjustment. I don't know what to call it, it isn't exactly a demand factor either, it is just an allowance for specific situations that allows you to use conductors at a different rating than their usual rating and is allowed for service as well as feeder conductors - if used to supply the entire load of an individual dwelling.

          If you are not supplying the entire load of an individual dwelling with conductor in question, this allowance means nothing.
          I live for today, I'm just a day behind.

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            #50
            Originally posted by kwired View Post
            You are reviving something that hasn't had a post for about 4 months so I may be missing something, but I did say "unless 310.15(B)(7) applies". Without the allowances of (B)(7) 4/0 aluminum only has an ampacity of 180 and 2/0 copper only has an ampacity of 175.

            What (B)(7) does isn't exactly an ampacity adjustment. I don't know what to call it, it isn't exactly a demand factor either, it is just an allowance for specific situations that allows you to use conductors at a different rating than their usual rating and is allowed for service as well as feeder conductors - if used to supply the entire load of an individual dwelling.

            If you are not supplying the entire load of an individual dwelling with conductor in question, this allowance means nothing.
            Thank you for responding I just learn something new what I did not see before
            But I am still confused how it is allowed to install 100A tap to 200A service unless there is not possible to overload that service in the future if someone see empty space in panel will use it to max 250-300A on residential that is less likely but commercial maybe....


            Sent from my iPhone using Tapatalk

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              #51
              Originally posted by Malywr View Post
              Thank you for responding I just learn something new what I did not see before
              But I am still confused how it is allowed to install 100A tap to 200A service unless there is not possible to overload that service in the future if someone see empty space in panel will use it to max 250-300A on residential that is less likely but commercial maybe....


              Sent from my iPhone using Tapatalk
              See 230.90(A) Exception 3. I suppose that exception could be thought of as a "loophole" but I have never heard of any problems. In those cases the overload protection is provided by load calcs and the fact that NEC calcs are very conservative.
              Ethan Brush - East West Electric. NY, WA. MA

              "You can't generalize"

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                #52
                Originally posted by Malywr View Post
                Thank you for responding I just learn something new what I did not see before
                But I am still confused how it is allowed to install 100A tap to 200A service unless there is not possible to overload that service in the future if someone see empty space in panel will use it to max 250-300A on residential that is less likely but commercial maybe....


                Sent from my iPhone using Tapatalk
                See section EF mentioned.

                Been that way for a long time. Sort of doesn't seem right, but single service disconnect - must protect conductors at least to their rated ampacity. Multiple service disconnects - any common conductors only need to have ampacity to carry calculated load, individual "taps" to an individual OCPD still need protected at their ampacity. Next size up rule and allowances of 310.15(B)(7) can factor into that selection though.

                With this rule I have seen 4 apartment unit + house panel with 5-100 amp main breakers and only 4/0 aluminum supply conductor to the whole works. Load calculation says 4/0 has capacity needed. If you add more load to something like this, it is possible you do need to look into supply capacity, in said apartments it may need to be somewhat significant load you are adding. Like maybe if you add electric heat to each apartment - that could have significant effect on the total load calculation even though each individual 100 amp feeder can maybe handle your added load.
                I live for today, I'm just a day behind.

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