This publication applies to – a.c. transmission, distribution and utilization systems and equipment for use in such systems with a standard frequency of 50 Hz having a nominal voltage above 100 V; – a.c. and d.c. traction systems; – a.c. and d.c. equipment having nominal voltages below 120 V a.c. or below 750 V d.c., the a.c. voltages being intended (but not exclusively) for 50 Hz applications; such equipment covers batteries (from primary or secondary cells), other power supply devices (a.c. or d.c.), electrical equipment (including industrial and communication), and appliances. NOTE Z1 Only standard frequency 50 Hz is used in Europe for public a.c. transmission and distribution systems. For systems and equipment at 60 Hz, see IEC 60038. This publication does not apply to voltages representing or transmitting signals or measured values. This publication does not apply to standard voltages of components and parts used within electrical devices or items of equipment. This publication specifies standard voltage values which are intended to serve - as preferential values for the nominal voltage of electrical supply systems, and - as reference values for equipment and system design. NOTE 1 Two main reasons have led to the values specified in this standard: The values of nominal voltage (or highest voltage for equipment) specified in this standard are mainly based on the historical development of electrical supply systems throughout the world, since these values turned out to be the most common ones, and have achieved worldwide recognition; The voltage ranges mentioned in this standard have been recognized to be the most appropriate ones as a basis for design and testing of electrical equipment and systems. NOTE 2 It is nevertheless the task of system and product standards to define appropriate testing values, testing conditions and acceptance criteria.