Care must be taken that the continuous voltage, and the peak voltage related to pulsed power situations, applied to a cable assembly is held below its maximum voltage rating. There are two separate voltage ratings for a cable – corona voltage and dielectric withstanding voltage:
- Corona is a voltage related phenomenon that causes noise generation, longterm dielectric degradation, and eventual failure. Thus, a maximum operating voltage must be less than the corona extinction level (extinction voltage) of the cable.
- The dielectric withstanding voltage, or dielectric strength of a cable, is a measure of the voltage level required to abruptly break down the cable dielectric.
To choose a cable for a particular application, determine the actual RMS voltage: Actual RMS Voltage = Peak Voltage Value/1.4. Then determine the effective RMS voltage by: Effective RMS Voltage = Actual RMS Voltage x √ VSRW. Select a cable with a maximum operating voltage value greater than the effective voltage.
As a cable assembly is used in a high altitude environment the maximum operating voltage is reduced as the lower atmospheric pressure leads to a reduction in dielectric strength in the termination.