main supply line "main supply line" means any high voltage or extra high voltage supply line for transmitting electricity from a generating station to another generating station or to a substation and includes any building or part of a building used in connection with such supply line; [Am. Act A1116 - Prior text read - ""main supply line" means any high voltage or extra high voltage supply line for transmitting energy from a generating station to another generating station or to a substation and includes any building or part of a building used in connection with such supply line;"] ACT 447 - ELECTRICITY SUPPLY ACT 1990 2. Interpretation.