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    Tap Rules

    Hello,

    Pretty new to line taps so I am interested in gaining some clarity.

    We have an array with a backfeed worth 85 amps. The easiest place to tap is in the ground onto a 100 amp circuit feeding a small guesthouse. The circuit is fed from a 200 amp bus of the meter/main.

    We would downsize the 200 amp main to a 150 to accommodate this.

    I am just wondering if this is legal. It seems like it is OK but I'm just making sure I am not missing something.

    thanks

    #2
    If you are connecting on the load side of the main disconnect then it won't be a line side interconnection.

    With an 85A AC inverter output you need to back feed an 85*1.25 OCPD, at least 106.25A in this case so you can't tap a circuit protected by a 100A CB in the main panel.

    Comment


      #3
      Originally posted by JoeNorm View Post
      Hello,

      Pretty new to line taps so I am interested in gaining some clarity.

      We have an array with a backfeed worth 85 amps. The easiest place to tap is in the ground onto a 100 amp circuit feeding a small guesthouse. The circuit is fed from a 200 amp bus of the meter/main.

      We would downsize the 200 amp main to a 150 to accommodate this.

      I am just wondering if this is legal. It seems like it is OK but I'm just making sure I am not missing something.

      thanks
      In order to do this...


      1) you'd need a 100A overcurrent device between the tap and the guesthouse subpanel, or at the subpanel

      2) 85A would have to be your calculated inverter output after the 125% multiplier that pv_noob explained, and the guesthouse breaker would have to be placed opposite the main breaker
      OR
      The main 200A panel could not have more than 100A of load breakers (per busbar) other than the guest house. You don't have to downsize the main for this option.

      Comment


        #4
        Clarification: the 85 amps is AFTER the multiplier, so that is the number.

        The guesthouse is fed from the meter/main to a 100 amp "main breaker" sub panel. The idea would be to tap this line, sounds like it is OK? In this case there would be no moving breakers as the main will not move and there are not really two sources in different locations here. That is the new part for me, I am used to landing in panels and the rules all make sense.

        So at the meter main, besides the 100 amp feed to guest house, there is also a 90 amp feed to a water system on the same busbar.

        thank you!

        Comment


          #5
          If you tap the 100A feeder then the 100A breaker in the main becomes your inverter output connection and is subject to the same rules as if it were just the inverter connection.

          If the 90A breaker is the only other breaker in the main then locations don't matter. You'd need the label or placard that says not to add more breakers.

          Comment


            #6
            Originally posted by JoeNorm View Post
            Hello,

            Pretty new to line taps so I am interested in gaining some clarity.

            We have an array with a backfeed worth 85 amps. The easiest place to tap is in the ground onto a 100 amp circuit feeding a small guesthouse. The circuit is fed from a 200 amp bus of the meter/main.

            We would downsize the 200 amp main to a 150 to accommodate this.

            I am just wondering if this is legal. It seems like it is OK but I'm just making sure I am not missing something.

            thanks
            Read 705.12(B) in the 2017 NEC or 705.12(D) in prior code cycles for load side tap rules.

            Comment


              #7
              Originally posted by ggunn View Post
              Read 705.12(B) in the 2017 NEC or 705.12(D) in prior code cycles for load side tap rules.

              Thank you, read them and they leave a lot to be desired.

              Since the only other breaker besides the guest house in the meter/main is a 90 amp, it sounds like I can get away with not downsizing the main. What is the code reference for this?

              Thanks

              Comment


                #8
                Originally posted by JoeNorm View Post
                Thank you, read them and they leave a lot to be desired.

                Since the only other breaker besides the guest house in the meter/main is a 90 amp, it sounds like I can get away with not downsizing the main. What is the code reference for this?

                Thanks
                Sorry, but without looking at a wiring diagram I can't make specific recommendations.

                Comment


                  #9
                  Originally posted by JoeNorm View Post
                  Thank you, read them and they leave a lot to be desired.

                  Since the only other breaker besides the guest house in the meter/main is a 90 amp, it sounds like I can get away with not downsizing the main. What is the code reference for this?

                  Thanks
                  I believe its ...(D)(2)(3)(c). It's the one that permits the sum of load a source overcurrent devices, other than the primary source overcurrent device, to be no more than the rating of the busbar. There's a required label that goes along with.

                  Comment

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