Current transformers (CTs) are typically installed on electrical equipment with potentially lethal high voltage levels.
Before installing a CT, read the Safety and Warning Notes from CT page.

Key Points

- Install CTs on the phase conductor that corresponds to the meter’s voltage input phase.
- Install CTs with the arrow(P1>P2) or label ‘This side toward source’ facing towards the breaker feeding the load.
- Connect the white(S1) and black(S2) CT leads to the corresponding CT input terminals with the white(S) and black(S2)dots.

Opening and Closing CTs

Ensure that the mating surfaces are clean when turning the split core CT on and off. 

Debris increases gaps and reduces accuracy.

Secure the CT to the conductor using cable ties around the conductor through the CT window.

To use a solid core CT, the phase conductor being measured must be disconnected at one end so that it can be passed through the hole in the CT. This is not difficult when the wire gauge is small, but becomes impractical with larger wire gauges and multiple parallel conductors.

Phase Conductors

For accurate measurements, the CT must be installed on the phase conductor that corresponds to the voltage input connection.

For example, a CT1 or ØA CT must be installed on the same phase conductor connected to the VA or ØA voltage input. Similarly, the CT2 or ØB CT is installed on the same phase as the VB or ØB voltage input, and the CT3 or ØC CT input is installed on the VC or ØC voltage input.

It can be helpful to use colored tape or labels to identify the wires.

To reduce magnetic interference between CTs on adjacent phases, it is recommended that they be separated by approximately 1 inch (25 mm). This helps prevent dust and debris from forming bridges across phase conductor terminals or bus bars and causing flashover arcing.

For best accuracy, the CT opening shouldn’t be more than 50% larger than the phase conductor. If the CT opening is much bigger than the conductor, position the conductor in the center in the CT opening. If that is not possible, try to position the conductor in the bottom of the ‘U’ shaped half of the CT, away from the opening end where there is magnetic flux leakage.

Plastic cable ties can be used to secure the position of the CT on the phase conductors. For some CT models, the cable ties can also be secured around the perimeter to prevent accidental opening

Orientation And Polarity

CTs are marked with a symbol (arrow) or label which indicates the correct mechanical orientation of the CT on the conductor being measured.

Find the arrow or label ‘This side towards source’ on the CT and install the CT with the label or arrow facing toward the current source: generally the utility meter or the circuit breaker.

In addition to installing CTs with the correct mechanical orientation, electrical polarity, as indicated by their white and black wires must also be correct.

Remember that both the physical orientation and the electrical polarity of each phase must be correct for proper operation.

CT Lead Wires

If the CT lead wire is longer than necessary, you can shorten it.

Short CT lead wires help minimize interference from electrical noise. 

If the CT lead wire needs to be longer than 8 feet, you can extend it. 

In general, it's better to install a sub-meter near the conductor you want to measure instead of extending the CT wire.


Metal conduit acts as a shield, but if you're using PVC, we recommend shielded twisted pair. 

If the distance is short, you can connect the power conductor for the meter's voltage input to the same conduit. 

However, over longer distances, you should avoid connecting the power conductor to the same conduit as the CT extension to minimize power line noise interfering with the sensitive CT signal.