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  • Consumption monitoring / CT in parallel

    My Sunpower AC Microinverter system just completed install. I asked for consumption monitoring at the contract... But it's not working yet.

    My home has two 200A service (Split 400A service). There are two 200A breakers at the service entrance. Each of these 200A breakers feeds it's own sub panel. (to be clear one of the 200A breakers had to be downsized to 175A because solar is feeing the associated sub-panel).

    Solar generation goes to the bottom of one of the 200A sub panels.

    The technician wired up a pair of CTs in parallel at the power entry to each sub-panel. But the results he got didn't make sense.

    Does anyone have a similar setup?

    Thanks for your advice and thoughts.

    Phil

  • #2
    I am not sure if this will work but if it will each set of CTs wired together would have to be on the same leg
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      I wonder, are these CTs intended to be "wired together"? The CTs and other equipment need to be a matched up set to work. Some
      CTs have a terminating resistor on the secondary designed to translate current to proportional voltage. This type would probably need
      to be in series, to give a total. In addition, if they are phased wrong (reversed), you will be subtracting instead of adding. Bruce Roe

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      • #4
        The post isn't really clear about what is going on. Generally, for consumption monitoring, you would want a CT on each hot leg... it sounds like that is what was installed. What was the technician seeing that didn't make sense? Want to post a picture of the installation, just to verify it looks correct?
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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        • ButchDeal
          ButchDeal commented
          Editing a comment
          they seem to be tying two sets of CTs (for the two different service panels) to a single MTU device. weather they are serial or parallel is not clear though.

      • #5
        ButchDeal has it right.... They have two sets of CTs in parallel into a single MTU. The data out didn't make sense.

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        • #6
          I would think that there would be a lot of nuances to trying to parallel CT sensors; making sure they're installed correctly would be imperative (eg., if one is backwards, it would cause weird readings because one would show incoming power but the other would show exported power, etc.)

          Here's some notes to keep in mind: http://www.ccontrolsys.com/w/Paralle...t_Transformers

          Me, personally - I built my own multiple-input openenergymonitor box using an arduino, and modified the arduino sketch to sum up the individual CT sensors. That way I can record the power used for each half-phase, as well as the sum used for them all.

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          • #7
            In order to account for current in 2 wires the CTs have to be wired in series, not parallel, and the polarity matters. Swap the polarity on one and if the output goes down then it was correct. If it goes up then it was wrong and leave it with the higher output.
            Last edited by JFinch57; 07-07-2016, 11:42 AM.
            Jeff, BSEE, 22.3KW, 45-240W w/M190, 46-260W w/M250

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            • #8
              I had mine just installed and and having the same issue. The output from these CTs does not make any sense.

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              • #9
                Hey philgrocks i have that same problem, where to install the CTs on my 400amp panel with two 200amp main breakers, can you tell me if you have it working? did you use 2 sets of CTs?


                Thank You Todd

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                • #10
                  Originally posted by 15FoxRzr View Post
                  Hey philgrocks i have that same problem, where to install the CTs on my 400amp panel with two 200amp main breakers, can you tell me if you have it working? did you use 2 sets of CTs?


                  Thank You Todd
                  If there is room to squeese the two wires together you can put two theough each CT. You just need to make sure they are the same phase. If not you will need two sets of CTs.
                  OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                  • #11
                    Thank you ButchDeal,
                    No I don't have enough room for the two wires through each CT, if I get 2 more CTs can I connect them together as long as the are on the same phase and arrows pointing towards the load? I have a Enphase Envoy and 2 CT-200 Current transformers. Or think I can buy 2 different brand CTs that will allow the 2 wires. Annual Degradation Factor

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