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A tractable method for accurately predicting the parasitic capacitance of a field coil as part of an all-fiber Mach-Zehnder interferometric switch based on Faraday rotation is reported. The effects of the wire insulation layer, inter-turn air gap as well as capacitive coupling to the four nearest adjacent turns are considered in predicting the effective parasitic capacitance for single-layer coils. The complex distributed capacitance network that results is resolved using Kron reduction to yield the equivalent shunt capacitance. Several coil configurations were designed and compared to experimental results. This new approach can be used in conjunction with existing expressions for inductance and loss to enable the complete and accurate a priori design of field generating coils.