Hochspannung fängt an, wo Signalspannung aufhört.

For cables U_max is the maximum DC voltage value or the peak value of the AC voltage. For sinusoidal voltages of rms 1 / SQR (2) the peak voltage) is. The test voltage of the cable is considerably higher.

For connectors must be made between the dielectric strength in completed connectors (counterpart plugged) and uncompleted connectors (open).
The dielectric strength at uncompleted connectors is much lower, since leakage currents can form the outside.
Example: SHV connector U_max completed 9 kV DC, not completed 3.5 kV DC.