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A microgrid (MG) is one way of integrating several low capacity renewable energy sources with a distribution grid. Multi-microgrids (MMG) originally proposed by the EU More Microgrids project can combine several MGs along with other distributed generation (DG) sources into the distribution grid. While different aspects of MMGs have been previously studied, a protection system design for it is yet to be explored. To design protection systems for MMGs, it is first necessary to study their fault characteristics. In this paper, we report on the fault analysis of an MMG consisting of two MGs, each made up of a diesel generator and a number of PV sources and wind generators. Fault analysis is carried out by simulating different fault types in the MMG with the distribution grid islanded from the transmission grid, and compared with fault currents in a single islanded MG. A theoretical analysis is also performed to verify the simulation results. The fault analysis results can be used to configure relay settings and to select the most appropriate circuit breakers and measurement devices for the MMG.