I need to know what does “Dielectric Withstanding Voltage” means in a high voltage resistor, as in a resistor the voltage is applied to its leads which are metal not dielectric.
In a capacitor, “Dielectric Withstanding Voltage” has a clear meaning because the voltage is applied across internal dielectric, but in a resistor what does it mean?
Most resistors, except for a straight wire, are build on a dielectric body and can suffer from dielectric breakdown, if the voltage rating is considerably exceeded. So the meaning is obvious, I think. With DC load, only high ohmic resistors are at breakdown risk, while low ohmic reach thermal overload first.
You are right, but what confusing me is that “Dielectric Withstanding Voltage” for a 40KV resistor (100MΩ) is only 700V or at most 1000V (as in manufacturers datasheet). does it mean the dielectric will damage in rated voltage? If no, what does it means?
Yes, that sounds confusing. In this case the specification is apparently designating a different property, i guess, the electrical strength of the encapsulation. But it should be explained in the datasheet.
Means that the maximum applied voltage is not to be calculated with Ohm law but must be a maximum that is written on the data sheet
Working with a voltage across the resistor that is above the maximum allowed will bring to arcing and surface currents that will destroy the resistor and probably also the electronics around
Also another question
A 100 MOhm resistor is a special resistor used in very special circuits and seems to me that a voltage of only 1000 V is too small
If you look at High Voltage resistor manufacturer, you will find high voltage resistor with resistance value more than 10GΩ (10,000 MΩ) and voltage ratings above 20,000 Volts. 100MΩ is completely practical in high voltage circuits.