Electrical insulation is not just a plastic polymer material that wraps wires, it is a complete system consisting of cable insulation, bushing insulators, space in the conduit, motors and general equipment. Mechanical pressure, pollution, and temperature changes can cause these components to deteriorate over time, causing current to leak. Current leakage will cause the following problems:

1. When the current passes through the insulating layer, heat is generated, which will deteriorate the insulating layer until the final insulation fails, and it will cause a fire hazard.

2. Leakage current must return to the source, it will flow through any available conductors, conduits, pipes, water or earth to return to the source. This unfavorable current can generate dangerous voltages.

3. Leakage current is not efficient. The current leaking through the insulating layer cannot drive the motor, emit light, or heat, but still consumes.

4. Leakage current will cause the overcurrent protection device to trip, causing the motor and transformer to overheat.

The result is that poor electrical insulation causes equipment failures and production line shutdowns. Now, no factory can withstand unplanned shutdowns.

Portable insulation testers generally output test voltages of 100V, 250V, 500V or 1000V. As in the piping system, the purpose is to provide a pressure (voltage) that is not particularly high. We want to find existing leaks, but we don't want to overstress the system and create new leaks. Lower voltages are used for low-voltage systems, such as telephones, networks, or control lines; higher pressures are used to test the insulation of power systems.

By testing the insulation resistance of different components in the system (transformers, switchgear, wires, motors), technicians can isolate and repair faulty components. Technicians use tests to verify the high insulation resistance between wires and ground or adjacent wires. Two common examples are testing the insulation between the motor windings and the motor base, and checking the resistance between the phase conductor and the ground wire/cage. Before powering on the system, use the insulation test to verify that it is sound and can improve the performance of the system; the insulation test can find manufacturing process problems and equipment defects, which are generally not found before the equipment fails. In the European Union, this test is mandatory, even for the smallest civil systems.