CT Sensor AWG


May be this is a dumb question but I want to be sure.

I have been reading about CT Sensor I am not sure if I can use it with a 6 or 8 AWG cable. I saw it dimensions 13mm x 13mm but Will It work with smaller cable?


Yes - you may notice small changes in the readings if the cable is not approximately centered in the aperture.

Really? How do you explain that?


The ‘single-turn’ case is rather denegerate since the ‘turn’ is just a conductor roughly co-axial with the CT magnetic path. The flux that needs capturing will prefer the CT core path since the reluctance is so much lower than air - but this ratio is finite and made worse by the inevitable residual air-gap from the jaw mechanism. So some flux will escape and hence not participate in the CT action. The geometry is non-linear - having the conductor path closer to one edge improves the coupling in that area, but is not exactly compensated by the worstening coupling to the now more distant face. For consistency, loosely packing the conductor to be roughly central in the aperture seems worth the trouble. You can verify the air-gap effect by simply squeezing the jaws tighter and seeing an apparent increase in reading across the burden.

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I’ve moved the conductor around inside the aperture, including twisting the core on the cable, and I’ve been unable to measure any consistent change. Whatever change there is has been completely swamped by variations in mains voltage. So it would seem that any inaccuracy due to the position of the primary conductor is insignificant, and much less than the manufacturing tolerance of the CT.

There is a significant risk of breaking the CT core, or of opening up an air gap, if ‘packing’ to centralise the conductor is not done extremely carefully. I would not recommend it, as the risk seems to far outweigh any advantage.

I can contribute some data I gathered from an experiment a while back. I tested moving the primary conductor around inside two CTs, one was the 333mV type I use and the other was the Current Cost CT analysed in this report: http://openenergymonitor.org/emon/sites/default/files/CurrentCost%20CT%20Report.pdf

My primary current was a stable 10A pure sine wave. Both CTs gave a rock solid output when the conductor was not moving and I recorded the following variations depending on where the conductor was inside the CT:

333mV type: median +/- 0.09%
CCost type: median +/- 0.7%


Thanks to everyone. Now it is clear.

@dbc Great job!