Why might insulation resistance measurements taken with a standard ohmmeter not be accurate?

Insulation resistance measurements are crucial for assessing the integrity of electrical insulation, and standard ohmmeters may not provide accurate readings for a variety of reasons.

Firstly, standard ohmmeters typically measure resistance by applying a low voltage. This is adequate for most resistive circuits but can lead to misleading readings when evaluating insulation resistance. Insulation will often not behave like a simple resistive load under low voltage conditions, and the accuracy of the readings can be compromised.

Additionally, when insulating materials are in good condition, they can exhibit extremely high resistance values, sometimes ranging into millions or even tens of millions of ohms. These very high values often exceed the measuring capability of standard ohmmeters, which are usually designed to measure lower resistances. As a result, the readings can be near the limit of the ohmmeter's range, resulting in inconsistency and inaccuracy.

Moreover, obtaining accurate insulation resistance measurements typically requires high voltage. Insulation materials need to be tested under conditions that simulate actual operating environments to ensure reliability. Low voltage testing may not adequately stress the insulation to reveal any potential faults.

All of these points highlight why relying solely on a standard ohmmeter can lead to inaccurate assessments of insulation quality, underscoring the importance of using appropriate