Instruments with insulation resistance measurement

Insulation resistance

— the ability to use the device to measure the resistance of dielectric materials, primarily the insulation of electrical wires.

As with a normal resistance measurement (see the relevant paragraph), the instrument applies a certain voltage to the item being tested and outputs resistance based on the current flowing at a given voltage. However, the mode of a conventional ohmmeter is not suitable for insulation — it has too high a resistance that requires appropriate voltages. Therefore, to work with dielectrics, a megohmmeter mode is required, in which the voltage on the probes reaches several thousand volts. Note that some devices may need to be connected to the mains (or even external equipment) to generate this voltage, while others cope “on their own”, due to pulse generators powered by conventional batteries. However, anyway, when working in this mode, special attention to safety is required (special probes, rubber gloves, increased care, etc.).