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The phenomenon of load currents with long decaying tails can be found on many pulsed-power generators, such as the Z accelerator at Sandia National Laboratories in the U.S. and the Angara-5-1 facility in Russia. In this paper, the reasons that cause the load current tail on the Qiangguang generator are investigated. The experiments were carried out using two insulator stacks with different diameters and insulator ring numbers. The results show that the current tail on the Qiangguang generator is not caused by measurement error but rather by electrical flashover across the surface of the insulator stack and by leakage current through the water between the stack and the outer wall of the water-filled transmission line that feeds the vacuum section on the Qiangguang generator. Also, an equivalent circuit for the Qiangguang generator was constructed and used in PSpice simulations. By adding a time-dependent resistance in parallel with the load, the simulations were able to produce current waveforms that closely match those recorded during experiments. In additional experiments, an optical fiber was used with a photoelectric cell to collect the flashover light emitted from the surface of the vacuum-insulator rings. The data collected show that the fiber signal and the beginning of the load current tail are time correlated. More recently, a new insulator stack made of Rexolite was acquired and used in yet more experiments. The results of these experiments show that, by using the new insulator stack, the onset of the load current tail phenomenon is significantly delayed. The data from all of the experiments show that stack flashover is the main cause of the load current tail on the Qiangguang generator.