Using Multiple CTs per phase

Depending on the model of WattsOn used, it is possible to use multiple CTs per phase. This is desirable when multiple conductors are used per phase and one CT is not large enough to encompass them all.

When using multiple mA CTs, the outputs are paralleled together to sum the individual conductor currents together. This method is accurate and acceptable, however, a few precautions must be observed:

  1. This method works only with mA CTs. DO NOT apply this method to 5A or 333mV meters/CTs
  2. The CTs must all be of the same type.
  3. The Meter must be configured for use with the particular CT type.
  4. The total current measured (ie: the SUM of all CTs) must be within the full scale rating of the meter
  5. Individual phase currents must be within individual CT maximum ratings.
  6. When using multiple CTs, it is imperative that they be oriented identically, and that the conductors are properly paralleled. The CT outputs must add together; if the polarity or orientation is reversed, the output signals will subtract from each other.
  7. It is imperative that CTs be correctly paralleled in relation to their phase. That is, do NOT mix CTs from different phases.

The CT outputs may be parallel connected in a convenient location, and one connecting wire should be brought into the WattsOn current input terminals. For quick connections, consider using an appropriately sized wire nut:

Although it is possible to use the terminal block itself as a termination point for multiple CTs, this is not recommended because of the relatively limited size, as well as potential for poor connection.

Using this method, the accuracy of the meter and CT combination is not affected.

Wiring Diagram:

Multiple CT Wiring Diagram