While waiting for new PCB I took some time to modify my CT calibration rig so I can hook up non-clamp type CTs. I had picked up a bag of HWCT-004’s on eBay awhile ago for about $2 each and didn’t expect much. I was pleasantly surprised.
They saturate at about 50A so good for most branch circuits. The linearity is easily less than 1% similar to the SCT-013, but the real difference is the low phase shift. As low as less than 0.5 at the low end and less than 0.2deg above ten amps. That’s practically negligible.
I have to confess that I don’t really know much about what determines phase shift. For the voltage sense transformers I have concluded that heavier transformers typically have less shift. With these, I don’t know if its the smaller hole, the fact that the core is continuous, or because the turns ratio is a low 1:1000.
The downside is that I’ll have to disconnect the wires from the circuit breakers to install. The upside is that they are so small, they will fit much better in the panel than the clamp on type.
I just ordered up a half-dozen other CTs on eBay. I’ll check them out and publish the results after they arrive in a few weeks (china post). Knowing the specs on the offerings out there should make it easier to shop for these things.