Why CT (Current Transformer) Direction Matters

 I have seen a lot of comments on Youtube videos and in forums that the direction of CT's don't matter as the current is reversing at 50Hz or 60Hz. This is fine assumption if you are just looking at the current waveform.

This is a 12.6A current waveform from a 30A/1V CT.



As you can tell the waveform goes back and forth as you would expect.

Here is a look at the same waveform but in the context of the 120V AC sine wave and as you can see the current (blue) goes up as the voltage (red) goes up. This is with a purely resistive load.



This is the same waveforms but with the CT reversed and as you can see here the current goes up as the voltage goes down.



If you synchronize your voltage and current waveforms (I.E take the measurements at the exact same time) you can then see if the signals are in phase which each other or out of phase by 180 degrees.
If they are in phase then the current is following one direction if they are out of phase then current is flowing in the opposite direction.

This is obviously simplified as most real world loads don't always a have a Power Factor of 1 and so you need to do more filtering but you get the point.

Equipment:

Siglent SH806 Portable Oscilloscope YHDC SCT013 30A/1V CT



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