Video: Installing Current Transformers - CT orientation with regard to either "H1" designation, Arrow, or White Dot



Current transformers should be oriented in a particular direction, with one side pointing toward the source of electricity (upstream or high side), and the other pointing toward the load (downstream or low side)

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Current Transformers

Metering and Power Monitoring

Current Transformers (CT's) may easily installed backwards on their respective load conductors. It saves time and money to ensure that they are installed with the correct orientation before energizing the load.

*Warning: Installation and maintenance of this device should only be performed by qualified, competent personnel that have appropriate training and experience with high voltage and current devices. Failure to follow the instructions / warnings in the Meter Installation Guide can result in permanent damage to the meter, severe injury or death.

CT's installed backwards provide inverted signals to the meters to which they are connected. Most meters note the polarity of the signal received from the current transformers, and use that polarity to help determine the direction of the flow of electricity, assigning a positive or negative value to calculated power and energy. It is imperative that current transformers are installed correctly with respect to their orientation on the load conductors that pass through them.

Most current transformers have at least some sort of indicator for orientation on the conductor, usually one of the following ways:

  1. "H1" - The H1 represents the primary current with a Line facing direction. A current transformer with "H1" printed on one side is usually intending for that H1 to be on the side of the CT when the energy is being provided from, generally referred to as the high side, utility side, line side, or source. These CT's may or may not also have an "H2" representing the side facing the load, or low side.
  2. Arrow - there may be an arrow on the current transformer which indicates the flow of power. These CT's should be installed such that the arrow is pointing toward the load to be measured. The Arrow points downstream, the load side, the low side.
  3. White Dot - Some CT's may have a white dot, or a dot of another color, like green, blue, or red. The dot only serves as an indication of the side of the current transformer intended to face the source of electricity, or line side, the high side. The dot should face that high side, the source of electricity.

Note: Certain low end meters only use an absolute value of the signal coming into the current input, so the orientation is often negligible in those cases. Meters of this type are generally incapable of discerning the difference between energy delivered into the load and energy received back from the load when that load acts as a source of power instead of as a user of power.