The Ring Bus is a three-phase ring bus installed in a full-height EMS module. It is used for the connection of the EMS motor/generator sets and loads as well as the protective relaying equipment for bus protection. The ring bus is opened at intervals by seven three-pole relays with normally open (NO) contacts. These relays can be operated by switches located on the front panel of the module or through the action of dc control relays or protective relays as part of a bus protection scheme. The module has a dc bus, energized from an external dc power supply, to distribute power to the relay coils. Three-pole circuit breakers are included at the bus bar as a safety backup in the event of extreme fault conditions.