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Investigations are being carried out into the use of superconductors as fault current limiters. The authors are investigating devices constructed from various high T/sub c/ materials. Of particular interest are limiters constructed from superconducting YBCO thick films on YSZ substrates. In order to predict the limiting characteristics of a fault current limiter and to optimise the design parameters, an accurate numerical simulation has been developed. This model includes measured data in the form of E-J characteristics, thermal properties and R-T data. Data sets for different materials can be selected in order to compare the performance of candidate materials. A major concern during limiting is the way that heat is generated in the superconducting film. The authors' simulation treats the superconductor and substrate as a number of small elements in order to determine the temperature distribution within the film and substrate. Further additions model the heat loss mechanisms to the surrounding environment. This thermal model is included in an overall FCL model, which includes voltage sources and line or load impedances. One can use this model to accurately predict the current-time waveforms achievable with typical limiters, and to easily explore the effect of a change in operating conditions.