The development of large-current-capacity AC superconducting cables is an important step in the realization of AC superconducting power apparatus. The authors have developed and tested a kA-class superconducting cable, bundled and twisted with 343 strands. The measured AC quench current was much smaller than the sum of the critical current of each strand. The authors theoretically and experimentally investigate the causes of this current degradation. Many factors were considered as the causes of this AC current degradation, and the focus is on the nonuniform current distribution among the strands of a cable was measured. The measured current distributions are compared with theoretical current distributions, and the component of AC quench current degradation is discussed.<<ETX>>