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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

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The lower frequency limit is defined by how many volt-seconds the core can handle without saturating out. Generally, the smaller the core, the higher the minimum frequency, since a higher frequency means smaller on-time and lower volt-seconds for the transformer to deal with.

(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.)

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  • \$\begingroup\$ Maybe add something about why you can't make the burden resistor arbitrarily low? \$\endgroup\$ – Spehro Pefhany Feb 26 '14 at 4:46

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