(a) Transmission system means all substances, lines, and appurtenances thereto used principally for interconnection or transfer of electricity from a primary source of power to a distribution substation (including any transformer other than a line transformer). In the case of power purchased, the point of delivery or receipt shall be considered a primary source. Transmission system shall also include high tension network conductors from the primary source of power to the primary side of the network transformers. If any lines or equipment operating at a voltage of less than 5,000 volts are included herein, a statement shall be filed with the commission describing such lines or equipment in detail and stating the reasons for classifying them as transmission items.

(b) Distribution system means all substations, lines, and appurtenances thereto used principally for the transfer of electricity from the generating station or the transmission system to the service connection leading to premises of consumers, including the distribution substations. If any lines or equipment operating at a voltage in excess of 10,000 volts are included herein, a statement shall be filed with the commission describing such lines or equipment in detail and stating the reasons for classifying them as distribution items.