A method for determining the effects induced within shielded cables by a high-altitude nuclear electromagnetic pulse (EMP), represented as a plane wave, is presented. The cable is regarded as a multiconductor line in which the EMP sources are impressed on the shield. An efficient matrix procedure permits simultaneous calculation of transient voltages and currents at any point on each conductor. This procedure, which is based on transmission-line theory, involves modal propagation and reflection matrix operators. The method of analysis permits fast calculation of voltage and current in the shield and inner conductor, whatever the terminal impedance may be. Comparison of the results obtained by applying the single and the multiconductor approaches reveals a few significant differences in the case of the braided-shield cables which become more important as lengths increase, as well as in given closing conditions.