$U_n$ is the rated phase-to-phase voltage of the cable. $U_m$ is the highest voltage for the equipment and $U_0$ is the test voltage (values from the standards listed below).

The rated voltage of a cable is limited to the choices below. However, when laid in a project, the operating voltage of every cable system can be chosen arbitrary in the range between 0.4 to 500 kV AC (1 to 5 kV DC).

Symbol
$U_{\mathrm{n}}$
Unit
kV
Choices
Id$U_n$$U_m$$U_0$Standard
0.4400 V440 V230 VDIN VDE 0298-3
0.5500 V550 V300 VDIN VDE 0298-3
0.75750 V825 V450 VDIN VDE 0298-3
1.01 kV1.2 kV0.6 kVIEC 60502-1 Ed.2.1
3.03 kV3.6 kV1.8 kVIEC 60502-1 Ed.2.1
6.06 kV7.2 kV3.6 kVIEC 60502-2 Ed.3.0
10.010 kV12 kV6 kVIEC 60502-2 Ed.3.0
15.015 kV17.5 kV8.7 kVIEC 60502-2 Ed.3.0
20.020 kV24 kV12 kVIEC 60502-2 Ed.3.0
30.030 kV36 kV18 kVIEC 60502-2 Ed.3.0
45.045 kV52 kV26 kVIEC 60840 Ed.4.0
60.060 kV72.5 kV36 kVIEC 60840 Ed.4.0
110.0110 kV123 kV64 kVIEC 60840 Ed.4.0
132.0132 kV145 kV76 kVIEC 60840 Ed.4.0
150.0150 kV170 kV87 kVIEC 60840 Ed.4.0
220.0220 kV245 kV127 kVIEC 62067 Ed.2.0
280.0280 kV300 kV160 kVIEC 62067 Ed.2.0
330.0330 kV362 kV190 kVIEC 62067 Ed.2.0
380.0380 kV420 kV220 kVIEC 62067 Ed.2.0
500.0500 kV550 kV290 kVIEC 62067 Ed.2.0