電纜額定電壓的選擇 Voltage designation
　　 電纜額定電壓應適合于電纜的系統的運行狀況，用U₀/U（U_m）表示，均為有效值，單位為kv
　　 U₀- 電纜設計用導體與屏蔽或金屬套之間的額定工作電壓；
　　 U—電纜設計用導體之間的額定工頻電壓；
　　 U_m –設備可承受的“最高系統”電壓的最大值。
The rated voltage of the cable for a given application shall be suitable for the operating condition in the system in which the cable is used , and is expressed in the form of U₀/U（U_m）are applied to the system voltages and running state , and expressed in the form U₀/Ukv.
U₀-The rated power-frequency voltage between conductor and earth or metallic screen ,for which the cable designed .
U-The rated power –frequency voltage between conductors for which the cable designed.
U_m- –The maximum value of “the highest system voltage ”for which the equipment may be used.

三相系統用電纜的U₀值推薦如下表：
The values U₀ recommended for cables to be used in three-phase systems are listed below: