Depends what the thermal rating and ambient temperature of the CT is. If this is an IEEE C57.13 transformer (and I'm guessing not based on the ratings), standard rating factors will be 1.0, 1.33, 1.5, 2.0, 3.0, and 4.0 at 30 degrees C. In this instance, the CT is required to have an RF of at least 2.0 and ambient of 30 degrees C or lower to run continuously at 600 A. For your non-C57.13 CT, you will have to check with the nameplate, the build/design standard, or the manufacturer.