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Distance from Current Transformer (CT) to digital readout meter

Discussion in 'Electronic Components' started by [email protected], Jan 2, 2006.

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  1. Guest


    I would like to install a CT on an electrical service and connect it to
    a digital readout display (with a 5 amp input) 70 feet away using #14
    gage wires. The CT would have a primary of 100 amps and a secondary of
    5 amps (100:5). From what I have been reading is that I will not get a
    correct readout at the display because of the distance of the wire.

    My question is that if I use a CT that has an output of 4-20ma and a
    digital readout with a 4-20ma input, Will I still get an incorrect
    reading at the display do to the distance.

    Thanks in Advance
  2. A CT is a current-mode device, if you have a closed circuit on the
    reade the only problem you might have is too large a voltage drop in
    the primary if the secondary leads are too small...

    Where did you read about this problem?
  3. Ralph Mowery

    Ralph Mowery Guest

    If you use a 4-20 ma loop baring any electrical interferance you can run
    much longer than 70 feet. It depends on how much resistance the loop can
    stand before the supply voltage can not force 20 ma . Where I work we have
    hard telling how many loops like that using some 20 to 24 guage shielded

  4. The point you raise about voltage drop on the primary circuit is
    relevant, as a reason to consider using transducers. Although in
    practice a volt say, may be acceptable drop in most services. Keep in
    mind that the voltage seen by the primary is only about one twentieth
    of the secondary voltage for the 100/5 CT. You need to do the
    calculations and see if the design is suitable for the application.

    The accuracy problem Kevin referred to relates to the VA rating of the
    CT, is the maximum VA that the CT can supply to the secondary load
    whilst retaining its stated accuracy. The CT secondary load includes
    the impedance of the ammeter plus connecting leads plus secondary CT
    reistance. If the secondary load impedance is too high then the CT
    iron saturates (partially or even fully) and the CT ratio ceases to be
    related to the turns ratio.

    Peter Dettmann
  5. Guest

    Thanks, I have ordered 2 Solidyne CT-100 for Solidyne with a 4-20ma
    output and 2 digital meters from another company that will take a 4-20
    ma input. Will replay back to this group/message when they are
    installed to let all know how they work.
    Again Thanks for the help.
  6. Guest

    I have installed the CT's but the company I order the panel meters from
    said they do not make a 4-20 ma input LED panel meter any more.
    Does any one know where I can get a 4-20 ma LED digital panel meter
    that is about 3 by 2 by 3 for around $20.00

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