An insulation resistance test is conducted to examine the effectiveness of insulation in a variety of electrical power system apparatus. Faulty electrical insulation is the source of dangerous shock hazards and can often cause ancillary damage to adjacent equipment as well. Routine electrical testing and maintenance can help to identify when insulation has deteriated before it reaches the point of failure, saving the expense of repairs and unplanned outages.
An insulation test is done by applying a high DC voltage to a conductor and measuring the magnitude of leakage current through the insulation. The resistance of the insulation is then calculated and displayed on the instrument being used for the measurement. It is the integrity of this insulation that protects energized conductors from ground or other energized conductors. Good insulation should have a very high resistance reading. Compromised or degraded insulation will result in lower resistance readings which warrant concern for the integrity of the insulation.
Much of the electrical power industry would refer to this test as a Megger test since they have in many ways pioneered insulation resistance testing. Megger is a leading manufacturer of portable test equipment and is well trusted for the quality and reliability of the product that it provides.
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Editor’s Note: This post was originally published in December, 2010 and has been updated freshness, accuracy and comprehensiveness.