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Technical Terms

Insulation resistance is the measure of a material's ability to prevent electrical current flow. While conductors like copper exhibit very low resistance, insulators (or dielectrics) such as rubber and glass possess extremely high resistance. In electronic circuits, maintaining high insulation resistance is essential to confine current to intended paths. Insulation failure can lead to leakage current, short circuits, and equipment malfunction, posing significant safety risks including electric shock.

To ensure safety and reliability, insulation resistance must be periodically measured to check for degradation. Since insulation resistance values are typically in the megaohm (MΩ) or gigaohm (GΩ) range, a specialized instrument known as an insulation tester or megohmmeter is used. The tester applies a high DC voltage (e.g., 250 V, 500 V, 1000 V) to the device under test and measures the resulting leakage current. The resistance is then calculated using Ohm's Law (R = V/I).

Conceptual diagram of insulation resistance and leakage current
Conceptual diagram of insulation resistance and leakage current | Technical Terms | Matsusada Precision