Per the title, what physical or construction parameters determine the frequency range of a current transformer? I happen to be looking at these two from mouser, but I'm sure the question is generic enough to apply to a large number of these things... What causes there to be a thousand-fold different in the minimum frequency?
Also, what happens if you attempt to measure a frequency well outside the rated range? For example, if you tried to measure a 50-60Hz residential power waveform with one of these KHz-range devices?
CT #1 : ICE CT08-1200 - listed as 40Hz - 200KHz
CT #2 : Murata 56200C - listed as 20KHz - 200KHz