In an electrical power distribution system, a ring main unit (RMU) is a factory assembled, metal enclosed set of switchgear used at the load connection points of a ring-type distribution network.
It includes in one unit to switches that can connect the load to either or both main conductors, and a fusible switch or circuit breaker and switch that feed a distribution transformer. The metal enclosed unit connects to the transformer either through a bus throat of standardised dimensions, or else through cables and is usually installed outdoors. Ring main cables enter and leave the cabinet. This type of switch gear is used for medium-voltage power distribution, from 7200 volts to about 36000 volts.