Generally the high voltage lines deliver electricity from Ireland's generation sources to the transformer stations, where the electricity voltage is reduced and taken onwards through the distribution system to individual customers' premises. There are also about 18 very large commercial customers directly connected to the transmission system.
EirGrid is the independent state-owned body licensed by the CER to act as transmission system operator (TSO) and is responsible for the operation, development and maintenance of the system. The TSO also offers terms and levies charges to market participants for the connection to and use of the transmission system, which are regulated by the CER. ESB Networks is licensed by the CER as the owner of the transmission system and is responsible for carrying out the maintenance and construction of the system.