Just wanted to add as an answer, since it wasn't covered in the original answer that for any commercially available current transformer, it should have an IEC rating of VA, and be marked so, or for IEEE transformers should have a "B-xx" rating.
For the IEC rated transformers, you have to select a burden resistor that is equal to or less than the VA rating to maintain accuracy. For IEEE transformers, you must select a burden resistor (technically, impedance) that is equal to or less than the 'xx' number. A B-2.0 rated device can handle up to two ohms burden load.
Probably about 95% of the small devices out there, with a primary rating of anywhere from 5 to 5000 amps are designed to handle a two ohm burden load, but that isn't a guarantee.