An important application for large-scale pulse power supplies (PPS) is electromagnetic launchers (EMLs). These de- vices utilized stored several MJs of electrochemical energy into linear mechanical energy. Because of extreme physical conditions, simulations are crucial in electromagnetic launcher (EML) research. As the operation risk rises, more en- ergy into the system adds weight to the model’s accuracy. In this paper, the electromagnetic impact of the bus structure is discovered in a recently developed EMFY-3 electromagnetic launcher, is presented. An H-shaped bus structure is used for the current injection. However, experiments showed that the H-shaped bus changes inductance calculations. A careful examination is made to reveal the physical reasoning behind the bus impact. We hypothesize that the rail portion surrounded with bus geometry has less inductance than the rest due to the eddy current created by rail current transients, which should be calculated carefully through numerical calculations, i.e., 3-D Finite Element Method (FEM). Two dif- ferent simulation models were constructed to test the hypothesis. Moreover, rail currents, breech, and muzzle voltages are measured to investigate electromagnetic calculations. Results showed a good agreement with experiments where the bus structure was modeled explicitly. That aspect showed that the bus structure should be well-examined when multiple PPS are connected.