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 two 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
standardized dimensions, or else through cables and is
usually installed outdoors.