This Standard specifies the nominal voltage value to be: The preferred value for the nominal voltage of the power supply system; The reference value for the equipment and system design. This Standard is applicable to: AC transmission, distribution, power systems and equipment with nominal voltage greater than 220V, standard frequency of 50Hz. AC and DC traction system. Equipment with rated voltage lower than 120V, standard frequency of 50Hz (but not absolutely limited), DC voltage less than 1500V. They include batteries (consist of primary battery and battery cell), other power supply units (AC or DC), electrical equipment (including industrial and communication), and electrical appliances.