OpenEnergyMonitor Community

Direction of current in the primary of a CT

This question is specifically in the context of a current meter using a CT.
Does the direction of current in the primary matter?
In transformer theory, whether it is additive or subtractive polarity, the voltage value across secondary is same (ignoring the phase). And in case of current meter, all we are interested in is the voltage value in the secondary. So does the direction of current in primary of the CT matter?
In case of CTs, where the direction is not printed or wrongly printed, should I be putting efforts to find the direction?

Hello @Onthe_Rocks and welcome! yes, if you are using a CT sensor in conjunction with an ACAC voltage adapter for mains voltage sensing then yes you will want to have the CT sensor connected the ‘right’ way. The voltage and current signals are sampled simultaneously and their combination gives a real power reading that is either positive with the power flow in one direction or negative if power is going in the opposite direction. An example could be a CT sensor clipped around the mains supply to a house with solar on the roof. When the house is importing from the grid it will read one polarity, when it is exporting it will be the opposite. Hope that makes sense?

Thanks for the info.
At the moment I am trying to build only a current meter (not a voltage plus current meter a.k.a power/energy meter). Essentially something equivalent of a clamp meter which can log data. I have a CT from an OEM which doesn’t have any markings. And as in the case of a clamp meter we don’t bother with the direction of the current, so was thinking do I need to bother finding the direction in my CT? I guess I need an analog meter to figure out the direction, which at the moment I don’t have.

No, you are correct, there is no need if you are monitoring current only.

Thanks a lot for the confirmation.