I have read that the load resistor on a current transformer should be as small as possible to retain the accuracy of the current transformer. Current transformers can output dangerously high output voltages if the output goes open circuit or the load resistor value is too high. For these two reasons I would suggest that you look at loading the CT with a resistor of a few ohms size (as opposed to K ohms size range) and then use an opamp circuit to amplify and offset the voltage across the resistor to the voltage range of the A/D converter. It can also be wise to introduce some type of protective device or clamp circuit into the input side of the opamp to protect it from high voltage accidents if the CT load resistor ever fractured or otherwise became open circuit.

Michael Karas