Overvoltage level describes the location of the equipment in the distribution network, the location of the different levels of overvoltage to withstand different levels,*** divided into four levels, also known as overvoltage category. Specific reference is made to IEC 60664.
--Overvoltage category I: the overvoltage to which equipment connected to circuits having measures for limiting transient overvoltages to a considerably lower level (e.g. electronic circuits with overvoltage protection) is subjected.
--Overvoltage category II: overvoltages on energy-consuming equipment supplied by a distribution unit (such equipment includes, for example, appliances, portable tools and other domestic and similar use loads). Overvoltage category III is used if the safety (reliability) and suitability of such equipment have special requirements;
--Overvoltage category II: equipment installed in distribution installations and whose safety (reliability) and suitability for use have to meet special requirements (such equipment includes, for example, switching appliances installed in distribution installations). Overvoltage category IV: overvoltage applied to equipment used at the power supply end of the distribution installation (such equipment includes, for example, meters and front-ranking overcurrent protection equipment);
We National standard: GB/T18481-2001 "power quality temporary overvoltage and transient overvoltage", Article 3.5 has a similar description. As follows: