Information about high voltage and its definition
High voltage starts where signal voltage stops.
For cables, U_max is the maximum permissible DC voltage value or the peak value of the AC voltage. For sinusoidal voltages, the rms value is 1/SQR(2) of the peak voltage). The test voltage of the cables is considerably higher.
For connectors, a distinction must be made between the withstand voltage for terminated connectors (counterpart plugged in) and non-terminated connectors (open).
The dielectric strength of non-terminated connectors is much lower because leakage currents can form on the outside.
Example: SHV-plugs U_max terminated 9 kV DC, non-terminated 3,5 kV DC.