Wiring Diagrams


The diagrams below show the typical wiring schematic for various types of CT,

  • Always follow the schematics and drawings issued for your particular installation
  • Always observe the polarity of the device that the CT is wired to

Measurement or Protection CT

Only a single phase can be measured by each CT

Core Balance or Earth Leakage Protection CT

All phases and the neutral should be passed through the CT, the EARTH must not be passed through the CT

Summation CT

Appendix A: Tightening Torques

Fastening TypeSizeMaximum Recommended Torque
Combi ScrewM40.9Nm
Binding Post – BrassM41Nm
Binding Post – BrassM61.6Nm
Split core CT banding7mm3Nm

Appendix B: Thermal Ratings

Icth: Continuous thermal current

Icth is the maximum current that the CT can be run at continuously.

Unless explicitly stated the continuous thermal current of our CTs is 100% of nominal primary current. Customers may request alternative ratings of Icth when ordering.

Ith: Short Time Thermal Current

Ith is the maximum excursion current the CT is rated to withstand for a specified time..

Ith is usually stated as 50 x Nominal current / for a duration of 1s (except for CT160 where we state In x10 / 1s) , this is the default but the customer can specify what they require at time of order if it needs to be different and we will design accordingly, this would be quite common on protective class CTs to have a specified fault current.