Insulation resistance measurement is a non-destructive measurement method when carried out under normal test conditions. It is accomplished by applying a DC voltage lower than that used for a dielectric test, and the purpose is to produce a result in kΩ, MΩ or GΩ. This resistance value expresses the quality of insulation between two conductive elements and gives a good indication as to the risk of leakage currents flowing.
Insulation measurements are carried out on new cables (not yet installed) at 250V or 500V, then at 50V or 100V for line fault reading on cables already in service. Measurements can be made between pairs of lines and the shield connected to the ground, or between the metal shield and ground.