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The three-phase four-wire drive system (4wEL) has been proved to be available of realizing fault-tolerant operation. However, this type of electric drive system (EDS) still has problems of higher current ripple than traditional three-wire EDSs. For a better understanding of the current ripple, a theoretical methodology of predicting the current-ripple in 4wEL is proposed for the first time. Based on the former study on traditional three-wire EDSs, the novel ripple prediction expression for the 4wEL is obtained by the study of corresponding voltage vectors and switching sectors. It is found that the prediction of current-ripple peak in 4wEL requires less calculation effort than in traditional three-phase EDSs. Besides, the difference of the current ripple peak between 4wEL and three-wire EDSs tend to be smaller for a lower modulation rate, while the variable duty cycle of the neutral phase of 4wEL can also influence the peak of current ripple. The theoretical prediction was also validated experimentally in a practical EDS and shows a proper accuracy of the current ripple prediction for both 4wEL and three-wire EDSs, which paves the path for the application of variable-switching-frequency PWM (VSFPWM) in 4wEL.