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CTs on bus bar versus wire

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  • CTs on bus bar versus wire

    Do CT's work around a bus bar compared to round wire conductors, or would there be some accuracy/calibration issue doing this?

    I am upgrading my meter main (load center combo) as part of my solar install. My new meter doesn't feed with wire, just bus bar (see pic).

    Screenshot 2020-10-04 123201.png

    I found this post where others have done this, but I'm curious about the results.
    https://www.solarpaneltalk.com/forum...in-panel/page2

    Also, side note, I am disgusted with the quality of Enphase CT's. Check out my second pic here where the clip snapped despite very carefully prying up to get it to open. Wow these clips are insanely thin, brittle, and worthless. CTs must stay completely closed to work properly, that much is for sure. Pathetic engineering here. I'll have to try and get a couple wraps of tape around it just to keep it shut now.

    IMG_3321.JPG

  • #2
    I find tape creeps, and that a zip tie may be better. Or glass filament strapping tape.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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    • #3
      I was also not impressed by the design of Enphase CT. I used Elfa utility knife to lift the clip.

      it might be problematic that CT directly touches bus bar vs insulated wire that electrically isolates CT and wire.

      Comment


      • #4
        You should be fairly accurate with a bus bar.

        Note that current transformers are not ideal elements. They try to put out a current proportional to the input but the characteristics of the iron inside them is non-linear enough to produce as much as 1% or more error from light load to heavy load. As long as you understand that limitation, you'll be fine.
        7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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        • #5
          The size and shape of the conductor through the CT do not matter, or if they might
          touch as long as no electrical path is formed. Yea, they are not as accurate as a
          shunt, but a lot easier to add to the circuit. Bruce Roe

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          • #6
            I agree - doesn't matter what shape the conductor is as it goes through the CT- whether it's rectangular, square, round, or many small round conductors. What matters is the current passes through the hole in the CT.
            All the CTs that I've dealt with (which is only a few manufacturers) have a non-conductive solid plastic on them. And that keeps the CT from touching the conductors going through it. So whether there's another layer of insulation (like around a wire) or not (like a bus bar) it doesn't matter. There's already a built in insulator that keeps the bus bar / wire from touching the working part of the CT.

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            • #7
              You should be ok using the CT on a bus bar. The critical area is making sure the CT is correctly oriented. Most have a little arrow or dot which is supposed to be pointing to the "load' side of the panel.

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              • #8
                Originally posted by SunEagle View Post
                You should be ok using the CT on a bus bar. The critical area is making sure the CT is correctly oriented. Most have a little arrow or dot which is supposed to be pointing to the "load' side of the panel.
                ok, in my case, the buss bar is AFTER all loads, between meter and load panel. So I point the arrows toward the loads still, right? "Direction of flow" would be direction FROM Power company TO my loads, correct?

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                • #9
                  Correct.
                  7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

                  Comment


                  • #10
                    Originally posted by dapug View Post
                    Do CT's work around a bus bar compared to round wire conductors, or would there be some accuracy/calibration issue doing this?

                    I am upgrading my meter main (load center combo) as part of my solar install. My new meter doesn't feed with wire, just bus bar (see pic).

                    Screenshot 2020-10-04 123201.png

                    I found this post where others have done this, but I'm curious about the results.
                    https://www.solarpaneltalk.com/forum...in-panel/page2

                    Also, side note, I am disgusted with the quality of Enphase CT's. Check out my second pic here where the clip snapped despite very carefully prying up to get it to open. Wow these clips are insanely thin, brittle, and worthless. CTs must stay completely closed to work properly, that much is for sure. Pathetic engineering here. I'll have to try and get a couple wraps of tape around it just to keep it shut now.

                    IMG_3321.JPG

                    CT's have multiple specifications.

                    The more common ones are:

                    voltage or current output

                    Accuracy class

                    Standard or Extended Range (range over which output is linear)

                    A 200:5 (200A to 5 A output) extended range will typically be used up to 400A

                    Burden -impedance of CT winding, wire and measuring instrument.

                    We typically use extended range, 0.3% accurate CT's with correct burden on commercial & utility revenue grade installations

                    Andy







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                    • #11
                      Originally posted by dapug View Post

                      ok, in my case, the buss bar is AFTER all loads, between meter and load panel. So I point the arrows toward the loads still, right? "Direction of flow" would be direction FROM Power company TO my loads, correct?
                      Correct. Your meter should reflect that set up with a positive kwh usage.

                      Comment


                      • #12
                        I agree - doesn't matter what shape the conductor is as it goes through the CT- whether it's rectangular, square, round, or many small round conductors. What matters is the current passes through the hole in the CT.
                        All the CTs that I've dealt with (which is only a few manufacturers) have a non-conductive solid plastic on them. And that keeps the CT from touching the conductors going through it. So whether there's another layer of insulation (like around a wire) or not (like a bus bar) it doesn't matter. There's already a built in insulator that keeps the bus bar / wire from touching the working part of the CT.

                        Comment

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