IEC 60502-1-2021 Power cables with extruded insulation and their accessories for rated voltages from 1 kV (U m = 1,2 kV) up to 30 kV (U m = 36 kV) – Part 1: Cables for rated voltages of 1 kV (U m = 1,2 kV) and 3 kV (U m = 3,6 kV).
4 Voltage designations and materials
4.1 Rated voltages
4.1.1 Rated AC voltages
The rated AC voltages U 0 /U (U m ) of the cables considered in this document are 0,6/1 (1 ,2) kV and 1 ,8/3 (3,6) kV.
NOTE 1 The voltages given above are the correct designations although in some countries other designations are used, e.g. 1 ,7/3 kV or 1 ,9/3,3 kV instead of 1 ,8/3 kV.
For the voltage designation of cables U 0 /U (U m ), the definitions in IEC 601 83 apply i.e.:
U 0 is the rated RMS power frequency voltage between conductor and earth or metal screen for which the cable is designed;
U is the rated RMS power frequency voltage between conductors for which the cable is designed;
U m is the maximum RMS power frequency voltage between conductors for which the cable is designed.
NOTE 2 U m is the highest voltage that can be sustained under normal operating conditions at any time and at any point in a system and excludes temporary voltage variations due to fault conditions and sudden disconnection of large loads.
The rated voltage of the cable for a given application shall be suitable for the operating conditions in the system in which the cable is used. To facilitate the selection of the cable, systems are divided into three categories according to the duration of time the system can be operated under earth fault conditions (see IEC 601 83):
– Category A: this category comprises those systems in which any phase conductor that comes in contact with earth or an earth conductor is disconnected from the system within 1 min.
– Category B: this category comprises those systems which, under fault conditions, are operated for a short time with one phase earthed. This period, in accordance with IEC 601 83, should, in general, not exceed 1 h. For cables covered by this document, a longer period, not exceeding 8 h on any occasion, can be tolerated. The total duration of earth faults in any year should not exceed 1 25 h.
– Category C: this category comprises all systems which do not fall into category A or B.
NOTE 3 In a system where an earth fault is not automatically and promptly isolated, the extra stresses on the insulation of cables during the earth fault reduce the life of the cables to a certain degree. If the system is expected to be operated fairly often with a permanent earth fault, it can be advisable to classify the system in Category C.
The values of U 0 recommended for cables to be used in three-phase systems are listed in Table 1 .IEC 60502-1 pdf download.