We apply the mode-matching method to the electrostatic analysis of shorted enclosed-cable trays that are generally used in industrial facilities such as a nuclear power plant. In mode-matching formulation on potential distribution, we utilize Laplace’s equation and superposition principle. After obtaining the modal coefficients from Dirichlet and Neumann boundary conditions, we then derive distributions of potential and electric field, capacitance matrix, effecive didlectric constant, and characteristic impedance to evaluate the electromagnetic influence caused by a short accident in the enclosed-cable tray.