Smart grids are playing a key role in modern electric power grids, improving load control, assuring safer operations and collecting valuable information of the electrical conditions of the grid. In a smart grid, a RTU (Remote Terminal Unit) is a device that is able to measure the electric variables of the grid and sends all the information to a MTU (Master Terminal Unit), which is responsible of controlling the operations of the grid. RMU (Ring Main Unit) devices are used in electric power grids to protect loads and to disconnect them in case of failure to prevent damage. This article presents the design of a special RMU capable of measuring voltage, current and frequency, detecting electric faults, and making automatic self-healing in order to manage the flow of energy in the smart grid to guarantee energy supply to the critical loads (hospitals). The RMU devices were installed on a scaled smart grid in order to show its operation capabilities.