The paper presents a mathematical model for analyzing the distribution of single-pole short-circuit currents (SCC) in passive parts (screens) of multi-system cable systems, consisting of single-core cables arranged in a triangular bundle. The aforementioned mathematical model is based on the method of equating a cable triple with a fictitious cable, using the method of mean geometric distances (SGU), with the application of the so-called matrix reduction coefficient, taking into account the electromagnetic coupling between neighboring cables (in the same cable trench). Based on the presented mathematical model, an appropriate computer program was developed, which was then applied to several different examples of multi-system cable lines.