Placing Multiple Current Transformers in a Single Channel

March 03, 2016

We didn’t say it was easy monitoring energy. While monitoring energy consumption, it may be overwhelming to manage numerous appliances using a power meter. To keep management simple, you can measure several different circuits by placing multiple current transformers within a single channel. However, this can only be done if all circuits are powered from the same phase of electrical circuits. This method is useful to combine all circuits into one measurement, oversee all appliances or to measure energy used for lighting. By placing multiple (2+) light circuits in a single current transformer (CT) you can capture more light circuits with bundled inputs. The maximum amount of CT’s per channel is limited to the gauge of the wire to fit in the terminal block. Placing multiple CT’s per channel has both its advantages and disadvantages:


  • Easily measure total amounts of energy the HVAC system uses
  • Reduce amount of channels usedsetra-power-meter-5
  • Increase cost savings from multiple meter expenses
  • Circuits can capture more loads
  • Save space
  • Less data points to monitor in BACnet



  • Not able to determine what area draws the most energy for efficiency decisions
  • Manual Calculations
    • Change your CT value by multiplying the amount of light circuits
  • Increase risk for error
    • Increase risk of running a circuit through a CT in the wrong direction or mixing up phases, which is difficult to detect
  • Lower Accuracy
    • Accuracy is fine when all loads are turned on and the current is high
    • Accuracy can be reduced when loads are off or in a low-power state

Installation Tips:

  • Install the CT on the circuit with the largest wire diameter and then add other circuits on the same phase
  • Be sure to thread all circuits through the CT's
    • The CT arrow or label "THIS SIDE TOWARD SOURCE" should face towards the current source, generally the utility meter or the circuit breaker
  • Place the CT’s parallel to one another, all circuits must pass through the CT in the same direction-towards the source of power
  • Increase the CT input in the software monitoring program
  • Use small gauge wires that are long enough to thread through the CT
  • Small gauge wires can be used with a combination of single phase and three phase circuits.


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Topics: Energy Management, Building Automation