# What determines the frequency range of a current transformer?

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

(Most CTs use ferrite cores, so if there isn't a specified $B_{max}$ you can try 0.22T and figure out what volt-second product you can achieve with your specified burden resistor.)