An insulation tester, also known as a megohmmeter, is an instrument used to measure the insulation
resistance of electrical wires, cables, transformers, and other components. Insulation resistance is the resistance of the insulating material, usually in the form of an insulating layer, between two conductive surfaces. Insulation testers work by applying a high voltage, usually between 250V and 1000V, across the insulation being tested, and measuring the resulting current flow. The insulation resistance is calculated based on Ohm’s law, which states that resistance is equal to voltage divided by current.