MOHAMMAD MAHDI Electronics Trading LLC

Insulation Resistance Tester (Part1)

About insulation resistance tester

Insulation Resistance Tester (Part1)


In electrical systems, we use insulating objects to separate the parts that carry the voltage current from other parts.

In reality, there is no absolute insulation and infinite insulation resistance, but the insulation resistance is relative and will change to that value by applying voltage. The voltage that is applied to the insulation and causes a large current to pass through the insulation is called the “breakdown voltage” of the insulation.

Types of insulation:

  1. Solid insulation (fabric – plastic – porcelain glazes and epoxy – mica – paper – glass – silicone)
  2. gas insulation (dry air – SF6 gas)
  3. Liquid insulation (oil)


In electrical equipment (cables, transformers, electric motors, generators, switches, etc.), insulation is one of the most important parts of the equipment. I use Insulation Resistance Tester  to measure the insulation resistance of electrical systems and equipment.


fluke 1507

Megger MIT525

Hioki IR4057-50


The factors that cause the destruction or reduction of resistance (aging) of an insulation:

  • Excessive heat of the equipment during work

The high heat of electrical equipment will gradually reduce the insulation resistance of the system

  • Mechanical factors and mechanical stresses created.
  • Environmental and chemical pollution.
  • Application of high momentary unwanted voltages to the insulation.

transient  voltages

The internal building of Insulation Resistance Tester:

Inside, there is a part for generating voltage, which produces a voltage according to the type and value of the working voltage of the tested equipment, and then the value of this voltage is connected to the insulating part of the equipment, and according to the amount of leakage current and according to Ohm’s law, the amount of insulation resistance will be measured.


A very important point and question the insulation resistance tester؟


What should we choose and what voltage level to test the insulation resistance tester of the electrical equipment in question?


To test the insulation resistance tester of the equipment in question, the selected voltage must be equal to the working voltage of the equipment. If there is a mistake in choosing this voltage , choose a higher working voltage, this voltage will damage the insulating parts of the equipment more.


In general, insulation and conductor parts in electrical equipment act like a capacitor, and the insulation of the equipment will have the same role as the dielectric of the capacitor.








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