Harris Institute of Technical Training

I have an installation that “they” say is 2 CT's wired in parallel feeding a 3S meter. I have not personally gone up the pole to verify, but I am trying to figure out the worst case scenario for a wiring mistake. I looked in your book 1, and assume it is wired like drawing 15 or 17. In my mind, if they wired 1 CT backwards you would only be metering the imbalance of the 2 -120V legs? I think I am trying to make it more difficult than it is.

Thanks for the question. Your thinking is correct. If they have mis-wired the CTs the meter would only be measuring the imbalance between the 2 – 120 volt legs and the 120 volt connected loads. Measuring the load imbalance can make it so the meter might be turning in the forward or reverse direction depending on which 120 volt leg has the most load on it (which will change directions as the load imbalance changes). The correctly wired CT and the 120 volt load flowing through it will drive the meter forward and the mis-wired CT and the load flowing through it will make the meter turn in the reverse direction and the imbalance between the two can result in either forward or reverse meter rotation. Also, any 240 volt load connected to this mis-wired CT meter set-up will completely be cancelled out. None of it will be measured. (If you find that the CTs are wired correctly by chance, please contact me because I might be able to offer another possible wiring error that would have similar meter error results).