During fault testing of a modular three phase power system for a mainframe computer an unexpected occurrence was observed. With four power modules installed, see Fig. 1, adding resistance to the neutral line caused the modules to latch-up. Though this behaviour was not a problem—the amount of resistance required to induce latch-up far exceeded the value that would occur in practice—it required an explanation and an assurance that it would not occur under more realistic conditions. To better understand the cause of the latch-up we attempted to simulate the power system using SPICE, a numerical circuit simulation tool. Modeling the system, however, proved to be difficult and ultimately unsuccessful. We then turned to Maple.