The following information on overvoltage categories is extracted from IEC 60664-1.Overvoltage category is a numeral defining a transient overvoltage condition.Equipment of overvoltage category IV is for use at the origin of the installation.NOTE 1 Examples of such equipment are electricity meters and primary overcurrent protection equipment.Equipment of overvoltage category III is equipment in fixed installations and for cases where the reliability and the availability of the equipment is subject to special requirements.NOTE 2 Examples of such equipment are switches in the fixed installation and equipment for industrial use with permanent connection to the fixed installation.Equipment of overvoltage category II is energy consuming equipment to be supplied from the fixed installation.NOTE 3 Examples of such equipment are appliances, portable tools and other household and similar loads.If such equipment is subjected to special requirements with regard to reliability and availability, overvoltage category III applies.Equipment of overvoltage category I is equipment for connection to circuits in which measures are taken to limit transient overvoltages to an appropriately low level.